Dunno what your Mac specs are, but Counter Strike seems like a good idea.. well, Counter Strike: Source that is. So get Half Life 2, great game.. and then once you've finished the single player campaign, go crazy online with Source. That's my 2 cents atleast.. with Doom 3, it's a good game but in my opinion the environment gets repetitive after awhile. There's only so much a dark and gloomy game can be before it starts to get repetitive, imo. Plus even on 2.5Ghz G5s the game still doesn't run anywhere near as good as high-end PCs.. and of course even on most PCs the game doesn't run super great. With Unreal (Tournament 2k4), it's also a good choice.. very multiplayer focused and pretty addictive. But yeah, I think HL2 (which comes with Counter Strike: Source) seems the best idea. Wait, is HL2 even out for Macs?