Well, I am a casual gamer who is not willing to give up my casual gaming.
I am certainly disappointed by the latest GPU offerings in the new iMacs. But if they play Madden '08, WoW, and Starcraft 2 reasonably well, I'll be happy.
(as a comparison, I happily played WoW (on reduced settings, of course) on my 1st gen 1.42Ghz G4 mini, 1.33Ghz G4 iBook (12"), and my 1st gen CD MacBook)
WoW runs on a GMA 950; the iMac GPU blows away the GMA 950.