I picked this game up on a whim one night after some friends had recommended it to me. Each "movie" has it's own unique characteristics about it, and are never the same twice. There are 4 playable characters in the Single Player mode of the game, but in the Multiplayer mode you can play the 4 main characters as well as the Special Infected.
My first encounter with a Special Infected was the Smoker. Smokers have a tell-tale wheezing cough. If you hear it, look out. They have amazingly long tongues and can ensnare you from quite a distance away. They can grab you and pull you towards them from directly ahead, either side and behind you. They can also grab you from above and leave you helplessly hanging for other zombies to attack you. When killed the also fill the air around them with thick gray smoke, which does clear after a bit.
The second infected is called a Boomer. You can tell a Boomer is near when you start hearing odd vomiting and regurgitating noises coming from your tv. Vile and disgusting, they vomit everywhere. If some lands on you it clouds your vision for a bit, and then slowly clears like the smoke. The bad thing about the bile they vomit is that it attracts the horde. The Boomers bile can also get on you if you are too close to it when killing it. Be prepared for a fight if you get this vomit on you.
My third encounter was with a Hunter. Hunters, unlike the Boomers with the vomiting sounds, have a distinct scream they emit. If you hear it, be on your guard. Lightning quick, dressed in black, the usually like to hang out around corners or dark areas waiting for you to walk near them. Out of nowhere, sometime it seems, they pounce and you're on the ground. The only way up from this is to have a teammate kill the Hunter.
Eventually, you'll come across a witch. Leave her alone. Her cry will sound like a child and it will tug at you to investigate. If you hear it, turn of your flashlight. It will only make her more mad. If disturbed, she is extremely fast and will knock you down. Keep shooting at her while you're down though.
Then, if you're unlucky, you'll happen across the Tank. He's big, he's mean, and relies solely on brute force. He will pick up large hunks of concrete and throw them at you and he can knock you back with a quick swipe. A handful of shotgun rounds should be enough to do him in.
The lesser enemy here, or greater, depending on how you look at it, is the Horde. They come in waves, seemingly never ending. Pipe bombs, car alarms...any loud noise will have you surrounded in seconds. Keep shooting and keep using melee and you'll make it through alive.
I primarily used the pump shotgun and the auto shotgun throughout the whole game. It does more damage and it some what of a long range weapon in the game. It does shoot farther then I think an actual shotgun can shoot though. There are more weapons though.
I found the game to be quite repetitive, but in a good way. You travel from point "A" to point "B" in each "movie". Like I said before though, no matter how many times you play the movie, it's never the same.
All in all, this game is a great MP game. If you aren't into MP, then you won't get the full experience out of this.