I have only recentley ditched my Xbox 360 for a PC. I thought at first I would regret that decision, but it turns out that it was the best gaming decision I've ever made. I never realized there were so many great free to play games with such great quality out there. Most free to play games that I'm going to talk about here have the option to pay for extra content , but its not required to get hours of fun gaming out of.
Age of Empires Online is my favorite by far. This game combines MMO style leveling system with awsome RTS gameplay. The only downside to this game is its play for free aspect. You can play for free as long as you want, but you wont be able to use the rare or epic equipment you find without paying for a premium civilization pack. You get to choose between playing Greeks or Egyptians, they are both different in there own ways, but essentaily they are the same. The only difference is what the units are called and how structures and people look. Your capital city serves as your "character" in the MMO aspect I mentioned earlier. You will recieve equipment for your units and upgrades to your palace as you level up. When you level up you get to spend XP on making your villagers harvest more resources or being able to upgrade your units in battle.
I personally got hooked on this game quick because of the gameplay and how there quest system works. The RTS gameplay feels just like your playing age of empires 2, but the graphics have a nice cartoony look to them which I didnt know if I liked at first. They grew on my very quick though, there is alot of attention to detail in this game. The free to play aspect of this game feels more like a demo than a full game, but I only played the free portion for maybe an hour then I had to buy the Premium Civilization because I was hooked.
Battlefield Play 4 Free is next on my list simply because you don't have to pay a dime for the full experience. You have the option to buy Battlepoints to use as currency to buy weapons to keep. If you choose not to buy the points you can use your xp you earn to rent out weapons for days at a time. The reason why I liked this game so much is because it feels like Battlefield in every sense. All vehicles are in the game like planes, tanks, jeeps etc. One issue that keeps the game from being more is that you only get 3 maps to play on. Then they dont let you choose what map to play on, you get thrown into a match. It dosent take to much away from the game for me because the maps that you get are classic Battlefield 2 maps. This game is worth it if you stick to the play for free side of the game, other wise everything seems overpriced.
These two games alone keep me entertained for hours and I didn't even pay 20 bucks. There are alot more games that are free to play on the PC that I wan't to talk about in a different article. There are so many good ones out there I've barely scratched the surface.