I don't play many games on my PowerBook because I already have two nice PC rigs plus a PS2. But I do know some local Mac Addicts that have dozens and dozens of modern looking games for their Macs. Ignoring the freeware games and all of the web/java/flash games, there are probably 250 real games for Mac OS X. Of the few dozen that I've seen, many look awesome. See the 9 links I posted above.
Mac users aren't exactly starving for games, but they don't have an overabudance either. Gaming on a Mac is kind of like buying your groceries at the Wal-Mart Supercenter, rather than buying them at a gigantic new Kroger, Safeway, or Albertsons supermarket. You still get the staples, there's still some good variety, but there's just not as much to choose from and some of the brands and styles look different.