Pro and cons fight over this title. Yes, you are again in a totally desert area. Yes, you start as noob even if you walked all the way from California to Nevada. Yes, after reaching the 15 level you can easily defeat all enemies (with the proper tactic and equipment). Yes there are no vehicles nor you can have more than two companion (well... Boone is more than enough).
BUT: from Oblivion there is the vegetation usage to make chems and healing potions (ehm.. stimpacks). There are much more types of endings and more complex story. There are the reloading benches (great idea!). There is the hardcore mode, totally challenging!
And, like Fallout 3, there are tons of great mods that enhance the game in every aspect (ops, sorry console users)!