What do you mean by "look the same"? If it's really just graphics, well yeah, the engine is more or less the same, but they are quite different games.

As someone who prefers FNV:

FNV is a lot grittier and fits better to earlier Fallouts that way. It leaves the player more choices (more companions, more decisions in quests that influence the story, just more stuff to do) and IMHO tells the grander story. Great DLC stories. Hardcore mode helps against the RPG-typical issue that the player character turns into a demi-god the environment doesn't react properly to.

It has a few more potentially game-breaking bugs, which is annoying, and you can tell that they planned for more content that they weren't given the time to finish, most other critiques IMHO apply to both games (graphics aren't great by modern standards, at some point you look to hard at the world and immersion just breaks, enemy AI and other mechanics don't help in that regard)

That said, you can get them for 10 bucks each with DLCs, so if you have the time it's worth trying both.