Diablo 2 generally runs great on Mac (unless you have Lion), however, sometimes I find it crash prone...
but Diablo 2 is a classic, I'd highly recommend it. But if you get it, get the battle chest as well (because Diablo 2 is way better with it's "Lord of Destruction" expansion pack). If you want to get into Diablo 2 now (since it's an old game), I wouldn't bother playing it without the expansion, quite frankly!