Normally I wouldn't mention it, but you say you're relatively new to gaming so... Metroid? Granted, those (the 2D ones, at least) are Nintendo/Super Nintendo/Gameboy Advance games, but the design philosophy is quite similar to Aquaria in many ways, and you could emulate them quite easily on OSX I imagine. Castlevania: Symphony of the Night is another, originally for Playstation, but also easy to emulate at this point (and it isn't too hard to find the actual disc if you have a Playstation or want to emulate it from a disc).
Unfortunately, I'm a die-hard PC guy, so I really don't know what's out there for OSX, though I imagine you'll *mostly* find PC games that have a mac port, rather than mac originals (I know there are some, but the market there has only really begun to open up more recently from what I understand). But I'm tired and kind of blanking. Hopefully other people are more useful than I am.
Anyway, if you're new to gaming and haven't ever given any Metroid games a shot, I'd definitely recommend trying them (it's really just a coincidence that my avatar and sig are based on them, heh).
