I just played a round of the Demo. It gives you the first two levels of the "Parish" campaign. Overall, I was pretty pleased with the experience. L4D vets can jump right into it, but at the same time there's things new enough to keep you interested. Impressions below, with some spoilers:

Spoiler Alert, click show to read: 
First off, new enemies. Some zombies, formerly police, have on riot gear and you have to turn around and hit them in the back to kill them. That's not too much trouble. But the Charger (who comes out of nowhere and bowls enemies over) is a bit of trouble, as it the Spitter, who releases a pool of acid on death that can do a lot of damage. The Jockey seems to be a Hunter clone where the only difference is that it rides you instead of pins you. Our old friends the Hunter, Boomer, Smoker, and Witch make appearances too. I didn't encounter a Tank.

There was one crescendo event, which we survived by the skin of our teeth. Maybe this was because I hadn't played it before, but as advertised, it seemed to be tougher than the previous crescendos in L4D1. Basically, you had to run through a security outpost to get to a bus station and the alarm in the tower goes off as soon as you enter. So you have to go through a small maze, climb the tower, and shut the alarm off just to stop the zombies from coming, and even then they don't freaking let up for a while. I ran out of auto-shotgun ammo about halfway through and had to switch to a hunting rifle to finish the rest of them off. By the end of it, we were all hurting and out of health. One of our party even died, but there was a conveniently-placed "Defribillator" item to revive them from death.

One gripe though - the much-advertised melee weapons are used in place of the much more useful pistols, so despite the options offered, I stuck with my guns (literally). Couldn't really get an idea that they'd be useful at all from the demo, especially considering you can still right-click to beat up enemies.


All in all I think the demo did its job. Looking forward to the release.