Whilst looking similar to the last Fallout, New Vegas in my opinion is superior over Fallout 3 in every single way, the story has vastly improved, with plenty of new features such as Iron sights and hardcore mode, and enemies that are much more difficult than those in Fallout 3, it is no longer possible to just waltz through the wasteland, in New Vegas, it's much more of a challenge. There are more "roleplay" mechanics like companions, crafting, and the removal of level scaling, and it has refined old mechanics like S.P.E.C.I.A.L and tweaking the effects of various skills like big guns. Whilst glitchy in some places, I believe that Obsidian are planning on releasing some patches to fix those inconveniences. Whilst most people will write it off because of the lack of multiplayer, understand that the Fallout series has NEVER been a multiplayer, or co-op game, and it never will be. The graphics may look a little edgy, but blame Bethesda who used the Gamebyro engine, which looks years old (same engine used in Oblivion + Fallout 3) and Obsidian did the best with it that they could, remember that a majority of the Obsidian team are former members of Black Isle, the studio that created the original Fallout games.
It's a much better RPG, even if it's still largely a shooter.
Basically, in my opinion, it's what Fallout 3 should have been.