Apparently one of the reasons why L4D2 is a sequel is due to the engine upgrades. In particular -- zombies now fall to pieces. Whether this is worth upgrading the content from a $20 level pack to a $60 boxed copy is down to personal preference, but being able to remove limbs and watch a zombie's rib cage emerge as you shred the flesh from its chest definitely adds a little something extra to the experience. Having said that, when you're in the thick of a mini-finale, surrounded by the undead, the last thing you'll be doing is examining these sorts of details.
As we said during E3, the game plays identically to original. There isn't even a particularly noticeable graphics upgrade, if you ignore the dismemberment improvements. Is that a bad thing? Of course not. A bad game is a bad thing. This is just a good game, made again. With new characters, levels and some new features -- such as melee weapons and special infected.
The art design is slightly different, too -- the New Orleans levels which we played through seemed a lot more colorful than most of the campaigns in the original. Like Diablo III's change in artistic direction, this may polarize people, but we see it as a good thing. We suspect it may be something unique to the New Orleans level, if the single Swamp Fever screeny is anything to go by.
The campaign plays just like a Left 4 Dead campaign. Bounce from safe room to safe room, avoiding zombies in-between. Valve has changed up the last level of the campaign though -- and this will be true of all campaigns in the game -- by using the last level as a mega-finale. While in Left 4 Dead the last level would usually end with an epic climax, requiring you to defend an area until help arrives, Left 4 Dead 2 will involve "gauntlet" style levels.
Also, watch out for that Charger. He'll knock you into the sea if you so much as look at him funny -- and let's face it, an arm as big as his is going to draw looks. The Charger is a welcome inclusion to Left 4 Dead 2. People are so familiar with the special infected that one or two new enemies will get players anxious again.
Ultimately, that's one of the most important things Left 4 Dead 2 can do -- remove people from their safety zones. After playing the original for a few months, you begin to see the seams and puppet strings. Like watching your favorite horror movie over and over again, the scares don't scare anymore. If L4D2 can do that again -- have us peeking round every corner and jumping at every noise -- then maybe it will be worth the $60 price tag. We'll see if that's the case when the game launches this November.