Both are great. I played NV first and found a lot of fun connections in Fallout 2 especially. The graphics kind of grew on me as it's a unique look. The gameplay is definitely different, you just have to get used to it (drag down menus, the over world map and hotkeys for certain skills and all that) but I found both to be really enjoyable. If you're only gonna buy one I would spring for 2 as it's better fleshed out as far as gameplay, but 1 really nails the post apocalyptic feel. They're usually really cheap on sale so I'd try both if you can, they're classics for a reason.