Replying to Good Game's on a Mac?

So, I have a macbook pro but i never really used it to much (Facebook etc.)
Today i decided i want skyrim on my mac, as well i have it on my xbox i thought it would be cool to also play on my computer
Then i realized you cant do it, Theres no good games that i know about for mac. besides bioshock on app store but thats all i really know

so let me ask you.
What are some good games on a mac that are preferably RPG or MMORPG something like that but no runescape.