I pretty much did everything, killed everything and acquired everything in F:NV, played through it 4 times and have all save files up to the final mission.. Just waiting on Old World Blues. SO, decided to play F3 for a 3rd time (i have all the dlc).
I never went through the game to try and get everything so now I am! I'm 33hrs in, and just got to lvl 10 and just discovered Tenpenny Tower. I think i'm about ready to tackle at least one dlc (maybe Op Anchorage).
In summation: WOW, I forgot just how incredible this game is.. and compared to NV.. Hmm, F3 is like the sun and NV is like just a flare coming off of the sun.. that's how much F3 is better than NV. That being said, NV is amazing.
Oh yeah, so, i can't believe i'm 33+hrs in and i literally only skimmed the surface of F3!!