Zombie Apocalypse is a perfect example of how you can ruin a good concept.
The game contains a fair amount of variety to the zombies you'll be fighting; there's a fat construction worker, a zombie that pukes on the ground, as well as "the queen", which is an old lady that gives birth to bugs through what appears to be a vagina on her stomach (I kid you not). The days take place in 7 different environments which include a gas station, construction site and a carnival. The environments certainly look different, but play identically. There are 55 days in the game, which means that the environments are repeated to a huge degree.
Your character always has a chainsaw with him/her, and you also get a basic assault rifle. In each day, special weapons will periodically appear; these weapons include a flame thrower, shotgun, and the completely useless Molotov cocktails. Each day also gives you opportunities to rescue innocent victims by protecting them until a helicopter arrives. These rescuing sections aren't handled well, though; you'll hear the victim yell "Help!", but they almost always appear out of view, and there is no indication of where in the level the victim is located. If you manage to rescue a victim, you'll get a pink teddy bear that you can throw around as bait.
If you have the misfortune of playing Zombie Apocalypse, you might find yourself having a little bit of fun with the first few sections of the game, but that's only because the game's biggest flaw hasn't hit you like a ton of bricks just yet. The game's biggest flaw is by far the difficulty of it, which is generally ludicrously difficult. In most days, there are 200-300 zombies that you must kill. The zombies frequently spawn in such a way that you are surrounded. Couple that with the fact that you can't switch between your special weapon and regular assault rifle, and you've got yourself a game that will eat away at your sanity; the days from 50 and up feel like they last for an eternity.
You can play Zombie Apocalypse either alone, through local co-op or online co-op. The online co-op is mostly functional, with the occasional stutter during a chainsaw kill. If you managed to torture yourself through all 55 days and feel like you want to lose what little sanity you might have left, you can try some of the different modes that are unlocked. There's a chainsaw only mode, a turbo mode and blackout mode which has most of the level pitch black. None of these modes are worth more than five minutes or so, because their only purpose is to make an already frustrating game even more frustrating.
Zombie Apocalypse is a perfect example of how you can take a great concept and stomp on it with golf cleats until it no longer shows any resemblance of its former self. The first few days are decent because there aren't many zombies against you, but those few days are definitely not worth shelling out 800 Microsoft points for. Even if you're a big fan of zombie themed games, you should avoid Zombie Apocalypse to show the developers that this kind of garbage won't fly. Thanks for reading.