It's a lot to take in, so let's start at the beginning.
The Assassin's Creed franchise as a whole tells the story of the The Assassin Order, also known as the Brotherhood, and their enemies, the Templars. The two forces have been fighting a philosophical war for centuries: the Assassins believe in total freedom for all people, while the Templars believe true peace is achieved through establishing order. The war has been going on since 465 BC, but what we seen in the series started with the Hashashin and the Knights Templar during the Third Crusade. It's from this period that franchise draws its name with the Assassin Order's creed: Nothing is true, everything is permitted.
The conceit of the series is that you're not directly playing the assassins of each era. You're actually in control of their descendants in the modern day or near future. These descendants are using a machine called the Animus to connect to the genetic memories of the original assassins, living through their lives. The Animus was created by a large corporation called Abstergo Industries, which is actually the modern face of the Templar organization. Most games in the franchise have a modern day component, which range from simple loading screens to full missions for the modern day protagonist.
There's more to the overarching story of Assassin's Creed, including the First Civilization and the Apple of Eden, but none of that is really necessary if you're just starting out. The important thing to remember is you're delving into the genetic memories of modern people to relive the lives of their supercool assassin ancestors.
Most people would think that the best place to start would be the first Assassin's Creed. Those people would be wrong. Assassin's Creed kicks off the whole story, but it's a different game compared to its sequels. It's a much slower, more methodical game focused more on recreating a particular period of time than just letting the player feel cool.
There's two places to jump into Assassin's Creed. The first is Assassin's Creed II, which switches up of the slower play of Assassin's Creed with the "run like a chicken in a cool hoodie" play that defines the later games. I'd recommend starting here. Assassin's Creed II has stealth aspects, but it's not hard stealth like Ubisoft's earlier Splinter Cell game. Assassin's Creed II is a relatively cheap purchase; you can find it as a standalone release for PlayStation 3 and Xbox 360 or pick up the Ezio Trilogy (Assassin's Creed II, Assassin's Creed: Brotherhood, and Assassin's Creed Revelations).
ACII is still early in the story of Desmond Miles, a bartender who happens to be the descendant of four Assassin's Creed's protagonists. The beginning of the game has a short recap of what happened in the first game, so you won't be completely lost. Assassin's Creed II is also early enough that there aren't many additional mechanics to muddy the waters, like Brotherhood's additional assassins or Revelations' tower defense system.
Your other option is to jump all the way to Assassin's Creed IV: Black Flag, which will make it a bit harder to jump back to the older games. If you're beginning with the series on Xbox One or PlayStation 4, Assassin's Creed IV: Black Flag is the right choice. Black Flag is connected to the other series through Assassin's Creed III hero Connor Kenway, but the game largely stands on its own. In fact, Black Flag lays out a future for the series in which the modern day sections are largely unconnected, unlike the stories of Assassin's Creed through Assassin's Creed III.
If you decide to start with Black Flag, you need to realize that it has an entire nautical sailing system that's an integral part of the game. Sailing is unique to Assassin's Creed III, Assassin's Creed IV: Black Flag, and Assassin's Creed Rogue. It's a lot to take in and you may be better starting with Assassin's Creed II and moving forward.
Now that you've figured out where to start, where do you go from there? Below I've listed the rest of the games in the series with a brief synopsis, their chronological era, their Metacritic Score, and whether or not I think you should play it.
2007 | PlayStation 3, Xbox 360, PC
This is the first game in the series, taking place in the Holy Land (Jerusalem, Acre, Damascus) during the Third Crusade. You play Altair ibn-La'Ahad, a veteran assassin who screws up a mission, leaving him to demoted. After his demotion, Altair is tasked with killing nine Templars to regain his honor. This game established Assassin's Creed's distinctive look: the white hood and the gauntlet with the Hidden Blade. Assassin's Creed also marked the beginning of Desmond Miles' story, the modern day bartender who is kidnapped by Abstergo Industries and forced to relive his ancestors' memories in the Animus.
MetaScore: 81Should You Play It: Maybe, Just to see where it all began.
Buy It Here
2008 | Nintendo DS
The first Assassin's Creed spinoff details the earlier adventures of Altaïr Ibn-La'Ahad. In a series first, there's no modern day component, so the game takes place entirely from Altair's viewpoint. In addition to the three cities in Assassin's Creed, Chronicles adds Tyre and Aleppo. Unlike its big brother, Chronicle has limited stealth mechanics and focuses more on combat and puzzle elements.
MetaScore: 58Should You Play It: Nope.
Buy It Here
2009 | PlayStation Portable
Altair travels to Cyprus to eliminate more Templars. Bloodlines plays largely the same as its home console counterpart, but with some control changes to accommodate the PSP. This game heavily featured Maria Thorpe, a Templar who would eventually go on to become Altair's wife.
MetaScore: 63Should You Play It: Nope.
Buy It Here
2009 | PlayStation 3, Xbox 360, PC
This is the first game that starred Ezio Auditore da Firenze and it takes place in Italy during the height of the Renaissance. Players can explore Florence, Venice, Tuscany, and Forli in Ezio's quest for revenge against the Templar-backed Borgias. AC II is more dynamic than its predecessor; you'll spend far more time on the move as opposed to waiting patiently. This game introduced the Monteriggioni, Ezio's villa that you could upgrade and Leonardo Da Vinci, Ezio's friend who creates all of his cool gadgets. Desmond's story is picked up here as he's freed from Abstergo and meets up with the modern day version of the Assassin Order.
MetaScore: 91Should You Play It: YES.
Buy It Here or Here
2009 | Nintendo DS
Discovery is a 2.5D platformer that takes Ezio to Spain under the Spanish Inquisition. Mostly forgettable in the grand scheme of things, but Ezio does meet Christopher Columbus and assassinates Templar Tomas de Torquemada. Yay, famous people!
MetaScore: 69Should You Play It: Nope.
Buy It Here
2010 | PlayStation 3, Xbox 360, PC
Brotherhood picks up right where Assassin's Creed II ends, bringing Ezio to Rome in his ongoing quest to get his revenge on the Borgia family. With the help of assassin Niccolo Machiavelli, Ezio rebuilds the local Brotherhood, allowing him to call on other assassins in-game. A large part of the game requires you to attack Borgia towers to free areas of the city from Borgia influence, a feature that carries on into later games. In an expansion of his role, Desmond can leave the Animus at any time to explore the modern day Monteriggioni villa.
Brotherhood is the first Assassin's Creed game with a competitive multiplayer mode.
MetaScore: 90Should You Play It: Yep, Probably my favorite of the Ezio games.
Buy It Here or Here
2011 | PlayStation 3, Xbox 360, PC
Revelations features an older, wiser Ezio who comes to Constantinople in search of five keys that will unlock Altair's Library, where a relic is kept. While there, he becomes involved with the local Assassin Order, Ottoman politics, and a young Suleiman. Revelations expanded the Borgia towers system with the addition of a tower defense mini-game, where the Templars return to retake territory. It also adds the new Hookblade tool for getting around the city and the somewhat game-breaking Bomb system, which allows you to craft a variety of grenades with different effects. Ezio meets his future wife, Sofia Sartor, in Revelations.
Part of the game involves Ezio delving into the memories of Altair at the end of his life. Desmond, who's trapped in a coma in the real world, spends the game in the Black Room, a safe mode within the Animus.
MetaScore: 80Should You Play It: Yes, but mostly to finish off Ezio and Altair's stories.
Buy It Here or Here
2012 | PlayStation 3, Xbox 360, Wii U, PC
In Desmond's final game, we jump forward more than 200 years from Ezio's era to the American Revolution. Here, half-English, half-Native American Connor Kenway (Ratonhnhaké:ton in his native tongue) is inducted as an assassin in the fight against his father, Colonial Templar Grand Master Haytham Kenway. AC III takes place on the Eastern United States: New York, Boston, the Wilderness, and the Eastern Seaboard. The game also adds a nautical sailing system for the first time, with Connor becoming the captain of the Aquila. In a big change for the series, Assassin's Creed III allows you to parkour on trees. TREES!
MetaScore: 85Should You Play It: Maybe, despite having a better MetaScore than Revelations, III was a decisive game for the fanbase. Many hate it.
Buy It Here
2012 | PlayStation Vita
Liberation takes place concurrently with Connor's story and stars the series only female protagonist, Aveline de Grandpré. Aveline is a African-French assassin operating in Louisiana during the end of the French and Indian War (one part of the Seven Years' War... more on that later). Aveline's primary gameplay is based around three personas - Assassin, Lady, and Slave - that allow her to move around different areas with various abilities. Otherwise, it plays largely like Assassin's Creed III, with some changes for the PlayStation Vita's control scheme.
Liberation was re-released on PlayStation 3 and Xbox 360 as Assassin's Creed: Liberation HD.
MetaScore: 70Should You Play It: Maybe, for a change of pace, but Freedom Cry is better.
Buy It Here (HD is on PSN, Xbox Live, or Steam)
2013 | PlayStation 4, Xbox One, PlayStation 3, Xbox 360, Wii U, PC
The next game in the series jumps back to the era of Edward Kenway, Connor's grandfather. During the Golden Age of Piracy, Kenway lucks his way into a ship (the Jackdaw) and the familiar assassin outfit, only to find himself in the middle of a war between the Assassins and the Templars. Black Flag integrated the sailing system from Assassin's Creed III into the main game, allowing players to go from running on land to sailing on the ocean seamlessly. It also introduced additional mini-games like diving and whaling.
The modern day part of the game places you in the shoes of an unknown, faceless employee at Abstergo Industries, who like Edward, finds themselves in something much larger than they first thought.
MetaScore: 88Should You Play It: Oh, yeah. One of the best in the series.
Buy It Here
2013 | PlayStation 4, Xbox One, PlayStation 3, Xbox 360, PC
Freedom Cry is the DLC for Black Flag, but it also found itself as a standalone release. The side story follows the exploits of assassin Adewale, Edward Kenway's former quartermaster, more than a decade after the end of Black Flag. Adewale finds himself shipwrecked on the island of Saint Domingue, a French colony in the Caribbean. Being a former slave, Adewale attempts to empower the slaves in the area and bring them to freedom. Freedom Cry is a relatively short game featuring much of the same gameplay as Black Flag.
MetaScore: 88Should You Play It: Maybe, if you're looking for more Black Flag.
Buy It on PSN or Xbox Live
2013 | Mobile
Even before Edward Kenway roamed the high seas, Alonzo Batilla decided to become the most feared captain alive. Batilla is neither Assassin nor Templar, but he finds himself trapped between both sides. Pirates features no assassin gameplay whatsoever and is completely a sailing combat and ship management game. It features some story characters from Black Flag, including Blackbeard and Ben Hornigold, but you can skip it.
MetaScore: 67Should You Play It: Skip it. It's solid, but you have to really love Assassin's Creed
Buy It Here
2014 | PC, PlayStation 3, Xbox 360
This is the old-generation-only release for 2014. Players take control of Shay Cormac, a former assassin turned Templar assassin hunter. Shay's story takes place during the Seven Years' War and his quest makes him a contemporary of Haytham Kenway during his rise to power in the Colonies. The game is developed by Ubisoft Sofia and will utilize an improved version of Black Flag's gameplay. Rogue has no online play and the modern day side of the game actually focuses on the inner workings of the Templar organization Abstergo.
Should You Play It: Perhaps! Here's my review of the game and if you're looking for more Black Flag, Rogue is the game to play.
MetaScore: 72Pre-Order It Here
2014 | Xbox One, PlayStation 4, PC
Unity is the next-generation-only version of Assassin's Creed, built from the ground-up for the new consoles. French assassin Arno Dorian operates during the French Revolution, attempting to stop the Templars who would destroy the safety of the Paris. Unfortunately for Arno, his adoptive father is the local Templar Grand Master and his love interest Elise is a Templar herself. Unity adds a new Parkour system to the game, allowing Arno to get down from high buildings as easy as other protagonists could climb up. Unity also drops the competitive multiplayer for a drop-in/drop-out four-play coop experience.
MetaScore: 72Should You Play It: Maybe. Like I said in our review, it didn't come together all that well, but it's still a solid entry in the series. I'd put it above Assassin's Creed III.
Buy It Here