I just took it for a spin. Really, I prefer the old cast more than these guys. These guys are so... normal. There are some nice things like new weapons, melee weapons (which have disgustingly bad hit recognition) and some fairly interesting special infected but really... I'm glad I didn't buy this. Heck, half the time I can't even hear what everyone other than Coach says because they mumble and slur so much. The slang they use is incomprehensible for me too. Even now, I can't even tell you any interesting quotes I heard from it because well... nothing really grabbed my attention. All I know is the TF2 scout talks way too much, Leisure Suit Larry sounds like he's in a Western movie flick, the girl is inaudible and ignorable, and Coach likes to read stuff off of walls and notices.
The atmosphere is so totally different from the first L4D. Instead of fearing the zombie hordes, I actually find myself rushing headlong into them even on expert because it's so unbelievably easy, thanks to the ridiculously high drop rate ala Crash Course (which is also unbelievably easy). The music doesn't help things either, by being upbeat and funny instead of tense and forebearing. The daylight makes seeing everything way too easy, which also makes seeing all the graphical flaws really easy too. It also irks me that all the new special infected are so easy to kill, especially compared to the old ones. While a smoker and hunter can take several shotgun shells, the jockey and spitter both die to one or two. The charger is really anticlimatic as well. Dies way too easily for its size.
Case in point. How do people play L4D? They hug walls, never venture into the open unless it's clear, avoid standing in the middle of open roads, keep ears open for special infected sounds, stick together, generally be cautious. How I see the people playing L4D2 in the games I've joined? Run out into open areas, stand in the open blasting things, running up to all sorts of special infected with the melee weapons, not really caring about safety or teamwork at all other than the general "don't go too far away" rule. I guess that's what I hate most about the new game. It's just not tense any more. It's like playing Unreal Tournament.
I started looking for what made me love the first L4D: the AI director. I'm sure the AI director is at work somewhere in this new game, but it's so ignorable. so unnoticable. There's SO MUCH WEAPONS and drops everywhere that really, when in the first game if you found the tier two weapons early on you were piss happy, here it becomes something that doesn't even cross your mind as you see everything you need at every other corner. The zombies too. The zombie waves come so often and in so few numbers that I don't feel any spectacular use of the AI director at all.
TL;DR: I know a lot of you are hailing it as awesome and fun and maybe it is but I would not be getting this. Even if this came out before the original L4D, I still wouldn't have gotten this. Maybe if it was $2.50 like TF2.