Mass Effect was developed by Bioware, so I'd suggest Dragon Age: Origins, Mass Effect 2.
However; Oblivion ranks very high on my favorite RPG list and I do believe it's #1. (For me), followed by Fallout 3. Fallout: New Vegas isn't as good as I thought it'd be.
I'll post as I remember some more good ones.
The Witcher is very fun too.