Not too impressed with Crossover myself. Works for some things, like Internet Exploiter, but I definitely couldn't see it working for games. Especially not anything near today's games or those from five years back. Just too buggy and slow. I get much better speed from normal programs run in Parallels than I do with Crossover. Its a shame really, as I usually only need to run a few programs for checking web sites or minor other things. This had my hopes up.
If you're thinking of gaming, save your money and just install Bootcamp and a version of Windows. Maybe later on they can work the bugs and speed issues out, but for right now its just not worth it.