You've dealt with stray buses, desperate survivors, and crawling zombies, but the first level is far from over yet. After vaulting over the bus, you will find yourself in a parking lot with a bus to the left and a group of zombies freaking out to the right. Before going the obvious path to challenge the zombies on the right, move to the left and head down a very small crack between the bus and the wall. At the back of this small alley, you will find a collectible lollipop. These lollipops glow a golden hue and will be placed several times throughout each level. You will also find a normal lollipop around here.
When you move into the main area of the parking lot, a short cutscene will show zombies climbing the walls and trashing the cars. Amongst the chaos, a lone survivor will attempt to survive in the white van. You have to protect this survivor, or at least you will have to if you want a perfect record for the level, bonus coins, and even an Achievement/Trophy (rewarded for saving all of the survivors in the first level.) Run ahead into the crowd of zombies and challenge them head-on. You have to distract them from the survivor. Stay by the van in order to better defend it until you've cleared out most of the zombies from this area. A few stragglers will hang by the bus to the right. Head over and clear them out as well to save the survivor, and then approach him for your reward. He will be spirited away by the helicopter again.
Head into the back of the bus ahead, marked by a giant floating arrow. As you climb in, another bus driven by a zombie will ram into the side of your bus, sending you flying around as the bus tumbles onto its side. When Juliet climbs out of the wreckage of the bus, she will see another survivor being harassed by zombies. This one will be dangling from the rope of the rescue helicopter. Zombies will be clawing at him as he dangles and he will fall onto a light post, where he will cling waiting for help. You have to get in fast and distract those zombies from the survivor. Use sweeping saw attacks and dodge frequently to make quick work of the shambling undead.
As soon as you save the poor sap from the light post, though, seven zombies will pop out of the ground as he walks towards the rescue chopper. You will have to protect the poor guy again, but luckily there's a decent distance between the survivor and the newly-spawned zombies. Rush out ahead again and challenge them. Keep the zombies busy while the survivor walks past towards the gate ahead. Finish off the group of zombies and head to the gate yourself. You will have to saw through this gate just like the last few.
As you cross through the gate, the rescue helicopter will meet an untimely end and go crashing down in the park. You will, once again, have to protect the survivor while he walks forward through the lot. There will be a whopping 25 zombies in this area, though. This would be a good time to activate your Special and power yourself up. You can do this by hitting the R2 button or the RT trigger. This will effectively turn all of your hits into one-hit kills. If you can get a bunch of zombies grouped together while you swipe with your saw, you can get huge bonuses in this mode. Make good use of it and eliminate all of the zombies so that the survivor may pass safely through. When all of the action is done with, don't forget to grab the lollipop from the hood of the car in the middle left of the level.
When you finish off the first lot of enemies, a speeding car will come flying through the lot. Hit the Circle or B button quickly to dodge the car. It will smash into the bus ahead, opening up a path. First, you will have to kill the remaining eight zombies in the lot. This shouldn't be too tough. With this, you should be able to head through to the next area.