bit-tech.net have reviewed the Mac version of CrossOver Games (for Intel Macs only), and are very upbeat about it! In particular, they found that older games (2005 and earlier) using DirectX 8 are widely compatible, and many DirectX 9 games also run quite well. They also found that many older Win95/98 games that have issues with XP or Vista, may actually run better in CrossOver Games! It's largely with newer games and custom engines that more significant issues creep in.
As I mentioned before, many games aren't yet showing in the compatibility lists at the CrossOver Games site, but that doesn't mean they won't run. This review confirms that, and although CrossOver Games is still in its infancy it seems to be quite capable. With further development this could be turn out to be a real winner, and it doesn't even require a copy of Windows - just the purchase of CrossOver Games itself!
Although a purchase is required, this is still open source software based on Wine, covered by the GNU license, and still has plenty of development to go. It's up to the individual to decide whether they're prepared to pay for open source, and if so, whether this is the right choice for their gaming at this time. There is a free trial period, so you can at least give it a good evaluation. And bear in mind that financial support for open source developers does have benefits as it allows them to put more effort into the product (and donation based support is notoriously unreliable...)