On looks alone it's not even close. And I don't just mean graphically, I like fallout for it's humor and npc. But it is a drab world.. I put down fallout before I really should have because I got sick of sand. Off topic, I remember reading somewhere that they are set in the same universe- planet. Anyone know if that's true.
Yes, FO3 and FONV are set on the same planet. FO3 takes place in and around Washington D.C. FONV takes place in the Mohavi Desert, in the (fomrally) American west. It's a desert, and there aren't trees, and it's all rocks and sand. You just gotta be expecting that.
Fallout 1 and 2 took place there also, and in Fallout 2 there is a large part that takes place in Vegas. Was my favorite part of Fallout 2. In this respect Fallout: New Vegas, is kind of like the "real" sequal to Fallout 2. Fallout 3 had the Enclave and the Brotherhood of Steel, but it was in the east, and from Fallout 1 and 2, I had grown to like the desert and the New California Republic, and the Mohavi Desert Rangers. And New Vegas had Cassidy's daughter...and Marcus! Kind of svcked Marcus wouldn't join your party this time around, but at least Rose of Sharon did. And she's much better looking than her father

Oh wait. Did you mean Tamriel was the same planet as Fallout? No. I don't see how. No magic in Fallout, just radiation.