There are only two games in the series as of yet.

Origins, the first one, is pretty good. It drags in spots, but overall it's quite enjoyable. I like it a fair amount, but if you've limited time it does take a fairly long time to play (although I myself generally consider that a good thing). I wouldn't bother with Dragon Age II. It can be sort of interesting to play through once, combined with rather annoying, and that's about it.

That's a very biased opinion, though. If you prefer older roleplaying games, Origins is pretty good (though not as good as most of them and significantly more expensive, so you'd be better off picking up an older game you haven't played yet); if you like Mass Effect and so forth, you might like Dragon Age II.