I'm always surprised at how few good rpg's have been made. The same few (Baldur's Gate, Neverwinter Nights) keep getting released for various platforms.
I would suggest checking out the Mac download store and see what that ratings are look at reviews.
I am sure there are some good ones out there (I just don't have time for gaming any more with little children). Quite a few contemporary ones are faster than real-time and cartoonish. Game play might be really good.
Personally, I've always liked turn-based strategy.