The first thing to realize with Killing Floor is that you're getting a mod. A mod turned semi-pro and sold for twenty bucks on Steam. So don't expect any of the polish and personality that makes Left 4 Dead as good as it is. These animation and graphics are downright, um, passable. In fact, I have to wonder if the occasional spasms of slo-mo are such a good idea. And the chatty blokes in Killing Floor (they're Brits) don't say anything memorable, which would be hard considering they're all interchangeable character models. After ten minutes of listening to these guys announce they're reloading, you'll long for the dulcet tones of Killing Floor's siren, a hag who damages you through walls with her piercing screams.

But once you've come to terms with the tautology that this is what it is, you'll find Killing Floor an excellent addition to any library of zombie killing games. It doesn't copy from other games so much as sit in a broad space among them. Comparisons are in order. In terms of pacing and tone, Killing Floor is like the Nazi zombie mode in Call of Duty: World at War. But in terms of geography, it has more in common with the wider open areas of Left 4 Dead. However, since your goal is to survive waves of zombies, you're not under constant pressure to keep moving, which is a primary characteristic of Left 4 Dead. You're going to need to hunker down. Welding doors shut -- and keeping them welded while zombies pound down your weld job in conveniently displayed percentage increments -- is the key to securing a position. You don't want to get caught in the open. Invariably, you will, because the woman who resupplies your ammo and sells you bigger guns appears in random and distant spots between each wave. This gives the game a unique alternating rhythm of stand-offs and mad dashes.

True to the title, the game is all about hurriedly setting up killing zones, into which you funnel waves of attacking zombies. Of course, the zombies often won't cooperate, or you'll run out of ammo, or one of the guys on your team just sucks. Like all the best zombies movies, things go wrong. People die. Parties wipe. The undead overrun the earth. The alternative is that you get through all the waves and fight one of the goofiest bosses this side of a Capcom game. Where did that guy come from?

Killing Floor is mostly multiplayer only. Solo matches are sad affairs, as there are no friendly bots tagging along to lend firepower and bad pathfinding. The difficulty scales with the number of players, so two will do just as well as six. Six gets pretty epic. I've only tried it on a LAN, but considering this is the old Unreal engine, I'd be surprised if it didn't work smoothly online.

The weaponry is pretty straightforward, with a few flavors of guns that feed into a "perk" system. You'll level up perks, which are basically clusters of bonuses. A 10% here. A 20% there. Here a price discount, there an immunity to some particular zombie power. It does a great job of keeping you playing, because the goals aren't just "kill x zombies to get to level y". Instead, you need headshots with the crossbow, melee damage, flamethrower time, or welding experience. Or all of them if you want to be well-rounded.

Unfortunately, there seems to be some problems with the experience system as of the game's release. It's a bit hit-or-miss whether you'll get credit for your actions. Let's hope that gets ironed out soon, because nobody kills zombies out of a sense of altruism. Enlightened self-interest is a vital part of any zombie apocalypse.