i play the sims 2 on my imac with no prob...of course it's better if u're not playing at full resolution so that when you're going downtown where there are many other sims, it won't lagged too much...

farcry, company of heroes, oblivion also runs well, as long as you don't put every settings at ultra high. overall, you can pretty much play any games on the imac, but don't expect a cinematic gorgeous display...i say it's at the medium...

p/s: all games are run on windows through bootcamp...