Yes, there are a lot of good games for Macs, but the selection still isn't GREAT. I mean, it's good, though, but there are still a lot of good PC-only games out there.
--Tony Hawk's Pro Skater games are for Macs (the guy himself was even a spokesperson for iLife '04!)
--Halo is for Macs
--Counter Strike aren't for Macs
--Grand Theft Auto games aren't for Macs
--Farcry isn't for Macs
--Battlefield Vietnam isn't for Macs
--GCN, N64, PSX, and PS2 emulators aren't available for Macs (they're barely available for PCs, actually, but still to a greater extent than for Macs) The only good PSX emulator for Macs is a cancelled one called Virtual Game Station, but all it does is take the place of a PSX, not the games. You still actually have to physically own the game so you can insert the CD.
So, these are just a few examples.