Okay, I know it's been out for two days, but it just finished downloading on my 360 and Steam. Here's my review:
The demo has a lengthy intro video, which is awesome anyway. Once you get to the main menu you see many options including Solo, Co-op (just called Campaign) Survival, and scavange. You can only do Solo and Campaign, but at least you'll know what else to expect in a few days. The new infected come at random times while playing this two chapter demo, you'll see Spitters, Jockeys and even Chargers. Don't worry however, as the original 4 infected will show up too! (Slightly editted I might add.) You'll also see an Uncommon common infected wearing riot gear. The game still has L4D's "Get from point A to B" feel, but it seems more enjoyable in my own opinion.

As an added bonus, The jukebox in the first stage has Jonathan Coulton's "RE: You Brains." and many other songs on it.