I second Borderlands (but I played it on Xbox360). Dragon Age (not DAO2) is good, but not open world (but I played it on PC).
I'm a huge RPG fan and I love DA:Origins, i found DA:Awakening to be decent too.
When I tried the DA2 Demo I was really disappointed, and in the start of DA2 I had the same feeling, but as I played thru it I liked it more and more.
DA2 is a lot smaller game than DAO (I have ultimate edition) where it's only 7.5GB and DA Ultimate Edition is 24GB.
Where all dungeons are unique in DAO most dungeons in DA2 is very similar, I guess they have like 4-5 different dungeon models they use to to make all dungeons in the entire game.
Companions in DA2 does have less history than the ones in DA1 and the story in general is a bit less "epic" than in DAO, but it is still one of the better games I have played, altho not as great as DA:O
I tried to complete all quests in both DAO and DA2 and my first playthru on DAO was 81hrs (with Awakening) and DA2 was "only" 36HRS
These all run well on the MBA?
When it comes to performance I did play DAO in win7 and DA2 in MacOS, reports I've heard is that DAO ran very poorly in MacOS. DA2 runs pretty good on my MBP (1680x1050 res) the MBA is slower, but with lower res you should get decent results.
Torchlight. Torchlight. Torchlight. Did I say that enough? No? Torchlight. Think of it as a teaser/appetizer for Diablo 3...
Torchlight is RPG-ish, but not really an RPG, fun playing, massive mouse clicking and keyboard bashing, but almost no dialogue, choices that affects gameplay or history.
Torchlight will run great as it runs great on my aging macbook
As far as i know two worlds is really slow on anything except a beefy MacPro, so until they fix the game I guess we won't play it!