Game of the year
. Well maybe that's Fallout 3. Regardless this game was a massive success and changed the way people look at cooperative online play. I wouldn't be surprised if Valve released some new campaign levels and maps for online play.
colakid's gripes are fair but not universal. I will explain.
This game wasn't ever meant to have a story. It's a spoof of zombie films, did you not get that? From the level locations (hospital, cabin in the woods, farm), to the character dialogue ("game over man!"), to the corny movie posters, this is a parody of sorts. And we all know zombie flicks more often than not lack any real story.
The game is short. That is true. You say you completed each campaign in an hour? Try upping the difficulty! You must be playing on the easier settings if you're playing through it that fast. You wont be cruising through on Expert. Each time you play through the levels it is different. Tanks, witches, and the Horde spawn in unique locations, making each play through vary and rarely ever similar. So again, the game is short but Valve addressed this with the features mentioned above. On top of that, the campaign isn't the bread and butter of the game. I've played short games that lacked any online capabilities at all. This game does support online. Not just co-op with friends but an addicting deathmatch mode where you get to be the Horde, which is a total blast.
If you play this game alone, offline then you're missing out on one of the best multiplayer experiences this generation of consoles. Playing as a Boomer and sneaking up a group of people playing as the Survivors and puking on them, triggering an army of zombies whilst your Horde friends jump them from all directions cannot be rivaled by any other game. Just awesome.