Here are some videos from E3 for Left 4 Dead 2 beta version:
Part 1:
Part 2:
Part 3:
My impression? The Charger and wandering witch is really something, and the gameplay is somewhat different from before in that you can't camp in one place to fight off the horde in a panic event, aka the gauntlet. In other words, you're gonna have to run or else the the zombies will keep coming until they bury you. Also, the music's got a Southern twang to it - awesome, and the special infected have new soundpacks. The melee weapon is apparently a pickup like a gas/propane/oxygen tank and you drop it as soon as you switch to another item. Also the pistols have changed - you start off with something I think is a Heckler & Koch (or beretta, but berettas are much skinnier) and the second pistol is a Glock. The tier two weapons are also different from L4D's tier two weapons.
Some cons I thought while watching these videos were the fact that you have these incendiary bullets which to me seems out of place considering the fact that such bullets are never for sale through known venues like gunshops. Also, the zombies remind me of Team Fortress 2 as well as the building color - they oughta work on that.
Back to L4D, I was able to play with a laser sight mod - fukken awesome, but apparently it's only available if you play on doku's survival games... and he doesn't freely give his mods out... shame.