Okay, all the talk about matchmaking on PC aside, here are my impressions of the 360 version, copy-pasted from over at Eurogamer:
I was a little worried from videos that it was too fast-paced/arcadey. I am no longer worried. The pace is hectic and downright frightening at times (and having played four games of it now, I can tell you that the AI Director works, and sometimes seems downright devious, such as putting a Witch by the health packs we all needed right at the end). The 'boss' Infected can be terrifying when they catch you off guard, and the Tank and Witch take a beating before they go down.
The weapons aren't that varied, but they all feel good, especially the hunting rifle and the basic shotgun. The pipe bomb is the most fun to use, though. It beeps and flashes red and attracts a swarm of Infected to it before exploding. Controls on 360 are pretty great. Four different layouts (I picked the one that put Crouch on left stick), and an option for Southpaw if you need it. Movement (yours, and the enemies') is quick, much more in the vein of CounterStrike than Halo 3 or CoD4, which 360 players are more likely to be familiar with. The 360 version includes a 180 degree turn button, which I didn't use often but was thankful for at times. The game feels great on the whole, and looks pretty good too. More importantly, it runs very smoothly, even when there are thirty or forty Infected on screen. Not that I counted. I didn't have time.
Vitally, the game absolutely encourages you to be cooperative. Stragglers are often caught by Smokers or Hunters, and you are very vulnerable by yourself, as a teammate is needed to rescue you from those attacks, when you are downed, and to guard you when you are blinded by a Boomer (which is very disorienting, and terrifying because it attracts Infected to your position). All of my games were with complete strangers, and in all of them we ended up laughing together... usually in relief after a particularly fraught moment, or when someone got caught unawares. Everyone I played with was grateful for healing or advice. The one time we had a teammate without a mic who charged ahead and didn't listen it was a much more frustrating experience. But playing with friends shouldn't be an issue. There's also a pretty smart 'Vocalize' command that shouts at whoever you're aiming (or shouts out a boss Infected) but it's not as useful as just talking into the headset.
I played all my games on Advanced, which is between Normal and the top level, which I think is Expert, and it was a very satisfying challenge: out of the four games, we had to restart from a checkpoint twice, and in all four we finished with at least half the team seriously injured. I can't imagine what Expert is like. Incidentally, the animation and speech for injured teammates are very impressive and immersive. In fact, the sound design throughout is great, and you can often tell what's ahead by listening carefully.
I am not sure if the game will get tedious in the long term: there are only two levels from one campaign on offer here, and they were different enough in placement of zombies and weapons each time to not feel like I was playing through the same areas again, although there are definitive chokepoints you become familiar with (especially the awesome final fight where you will probably be pretty wounded). I really, really want to play and see more, and particularly to play Versus mode, which is not included in the demo. But from what I can tell, there are many, many hours of multiplayer fun here; I'm
not sure what it would be like to play by yourself. 360 version also includes split-screen, and you can change in the menus which way the screen is divided (interestingly, you can also set colour settings for either TV or computer screen, which was useful for me playing on my 20" widescreen monitor, and I'd like to see it included in more games).
The only remotely frustrating element is your own vulnerability from Hunter/Smoker attacks, and when surrounded (you will spend a lot of time hammering the left trigger to shove zombies away from you or others), but that's by design. Being unable to help a teammate who's being roped to their death by a Smoker because you can't get through a pack of regular Infected has a nice quality of despair to it.
Based on what I have played, it's an EG 10.