(This review is for the PC version of the game. Nick has provided commentary on the 360 version at the end of the review.)
Coming a mere year after its predecessor, swathed in a dodgy boycott, you'd be certain to think that the sequel to last year's Co-Op Game of the Year would be a tough sell. Luckily, you'd be wrong. Dead wrong. In fact, Left 4 Dead 2 is so much better than the original, you might as well forget it existed.
You still grab three of your closest friends and fight your way through levels controlled by a sadistic "AI Director" using whatever weapons and items you can scrounge up to survive, but though the formula may be the same, Valve has delivered in three major ways:
Intensity.
While the original game had its fair share of "holy crap" moments, every single "movie" in L4D2's campaign has several moments that are so intense, you'd not be far off thinking they came from a Call of Duty title. Whether you're fighting through a burning building, monsoon-level rains that make it impossible to see more than a few yards in any direction, or scrambling to retrieve fuel for your escape vehicle, each scenario has something new and different to offer, which brings us to...
Variety.
Unlike the original game, the crescendo moments and finales are almost entirely unique to the level they're contained in. The goal of each scenario is still the same, navigate the area, reach safehouses, then somehow signal or acquire an escape vehicle, but the ways in which this occur are very different. Instead of having you hole up and defend a location each time you alert the horde, you might have to quickly ascend three floors of a shopping mall to find the security office, or run along roller coaster tracks.
The Jockey HATES Depeche Mode!
Speaking of which, each campaign "movie" is a unique setting, which stands in stark contrast to the original game. Whereas in the original you had alleyways of a nameless city, a generic airport, and a trek through some wood/farmlands, Left 4 Dead 2 uses its settings to great effect, finally bringing us to...
Personality.
Though only two of the four new survivors (Ellis is probably my new favorite survivor out of the whole bunch) are anywhere near as entertaining as the original cast, Left 4 Dead 2's personality is reflected in the new levels and enemies. When you find yourself in a carnival, you'll be attacked by insane clowns whose noses you can honk, or with some curious exploration you can find games in the midway that you can play (damn you, Mustachio!). The new "uncommon" infected add a lot of flavor, whether they're the aforementioned clowns or CEDA personnel in HAZMAT suits. The infected are designed to look like they fit in the levels you find them in, and it really helps immerse you in each locale.