I started with Fallout 3, which I bought because I'm a Bethesda fan. I hadn't heard of the series up until that point.
I borrowed Fallout 2 from a friend and I'm trying to get into it, I really am.
I'm one of those godless heretics who didn't hear about the series until Fallout 3.
I bought it because I was a big fan of Morrowind and Oblivion, and it didn't disappoint.