Initially, you start in a safe zone with weapons, ammunition and medical kits lying on the table. From here you can choose between a pump shotgun and an Uzi submachine gun. The Source engine can really put a trashy and cluttered feel to the surrounding environment. Because of this, one thing I noticed immediately is a white border color around any usable item you might be able to pick up. Once your team is ready, shoot any zombie reaching their arm through a window into your safe zone and get ready for the swarm.
Left 4 Dead (courtesy of l4d.com)
Once you step outside, things pick up rather quickly. Zombies come out of almost nowhere to attack you, but as long as you use team work, you can work your way out of sticky situations. Sometimes you may only come across a small batch of them, which drop pretty quickly, but if there's a swarm nearby, they'll converge on your group at a rapid pace. This obviously requires a great deal of communication and teamwork, but in the event of a zombie holocaust, there's also a time for "every man for himself". Fortunately, the secondary fire on your weapons is a fairly brutal melee swing, which came in handy a lot more than I thought it would. I'm really hoping they put a foot-kick in there as well.
Along with your standard firearms, there are also Molotov cocktails and pipe bombs. While I don't recall using the cocktails, I can definitely tell you that the pipe bomb produces a great deal of destruction. At one point my team and I were moving carefully through a fairly dark alley that dumps into a street at the end. In the middle of this street was a car, and from behind that car, running straight at us was a large swarm of bloodthirsty undead. Naturally, I felt this was a fantastic opportunity to throw my pipe bomb and watch the chunks fly. Not only did they fly, but a firestorm shot down the alleyway toward us, forcing us to retreat a bit so we weren't torched. Even still, the scorched and flaming, yet surviving zombies ran out of the inferno at us relentlessly and unfazed by the large explosion.
As the level progresses, you'll find yourself needing more ammunition and medical supplies. Fortunately, there's a cache or two of them the farther you get, including upgraded weapons such as an M16, scoped hunting rifle, and a semi-automatic shotgun. There's also a stack of pistols if you want to go akimbo style. Use this opportunity to make sure your teammates, and yourself are healed and ready for battle, because it only gets crazier from here.
If one of your teammates drops, they cannot get up until you go help "revive" them. This consists of walking over to their position, highlighted with a green outline, which you can see through at least one wall, and hitting "use" on them. You'll hear your character encourage them to get up and continue fighting the good fight. You can also heal them if necessary by equipping your medical kit and using it on them. Just make sure to save one for yourself. If you yourself have dropped, you'll find yourself lying on the ground, unable to move and only able to swivel around and file your pistol at anything nearby. This is especially terrifying if you're being beaten by a swarm of zombies, and if your teammates don't mow them down and find you quickly, you won't last long at all.
The zombies themselves are obviously fast and furious. The AI seems to be very zombie-like in several ways, being that if there's a horde of them, they're all seeking out your warm flesh. However, if you happen to come across a single zombie, there's a chance they'll be just standing there staring at the wall before they even notice you. Take every opportunity you can to cave their skull in with the butt of your rifle.
There are also "boss" zombies, which if you aren't careful, can give you a very bad day. The only ones I had any experience with were The Boomer, which can blind you with projectile vomit and explode when they are killed, The Smoker, who had a large tongue to tow you in and strangle you until one of your teammates can come to your rescue, and The Tank, which was a large meaty zombie that could destroy parts of the environment in the levels and lob large items at you. These were unplayable at the booth, and two of them at a time were operated by Turtle Rock Studios employees, but it was interesting watching their screen. While I couldn't tell exactly everything they did, one notable thing I did notice were these peculiar colored lines and arrows on the floor. I'm not sure if these lines directed a player to the position of the Survivor team, but this would make complete sense to me.
When a round is all said and done, a summary of the game will come up. There are awards given out to players much like the "Excellent" and "Impressive" awards bestowed on a player in Quake 3. The awards here are things such as "Savior", "Good Teammate", and "Self Tongue Stop", as well as what looked to be kill statistics and medical kits used.
All in all, I can't wait to get my hands on the full version of this. As a huge fan of fast and furious FPS gaming, cooperative game play, zombie holocausts, and the Source engine, there are few games that I am looking forward to more.