Don't let the rest of the responses here get you down. You got a pretty great machine, Macbooks just aren't widely known for their gaming abilities. When it comes to gaming I'm not one to really look at production computers. If you want to game, slowly piece together a respectable PC. You don't have to be a baller to get your game on. Unless you're trying to play Crysis, a dedicated gaming machine shouldn't cost more than $300-400 to build, sometimes even less if you look hard enough and be patient. Granted, that's not retail prices, that's straight used eBay & craigslist stuff but if it works, who cares where ya got it. I'd say get a year or two old components for cheap and get yourself a bad lil setup. Here's a quick off the top of my head idea:
256Mb vid card (this is where the bulk of your money is gonna go)
2 gigs of pc2-5300 or pc2-6400 ram (4 would be ideal, especially since it's so CHEAP these days)
Intel Core Duo or Dual Core processor (ain't always cheap either. again, used used used used is the way to go!)
abit or asus motherboard
Run XP pro on it and you're ready bro. You'll have the best of both worlds, a gaming PC for the house and a Macbook for portability and everything else you could need