Can you explain how? Nothing in these games is the same, apart from the fact you can explore, which other games can offer too.
It suffers from the same issues i had with oblivion, also it had more in common with oblivion than it does with the previous fallout games. A few similarities with oblivion i would list would be:
Very little attention to the main plot, the emphasis is on the open plan of the game, not the storyline itself. It just... ends.
Very frequently reoccurring NPC models, just like oblivion you can expect to see the same face multiple times.
Reasonably frequently reoccurring NPC voices, not quite as bad as the models, but you will hear the same voice actor playing the same guy several times
'The Famous Guy' Like oblivion it seems they invested a large portion of their cast budget into getting one famous actor into the credits who doesn't even stick around for long.
Annoying lock picking minigame; it's had reconstructive surgery, but it still there and still gets on my nuts.
First person; well, it is, oblivion was, fallout wasn't
Hand to hand combat pretty much exactly the same as oblivion but without shields, you can still block though.
Seemingly random monster leveling and very many seemingly random enemy encounters. Walking through the wasteland and oh, i'm getting attacked by an ogr... sorry i mean bandit.
The fact that combat is now largely real time with a bit o' turn based instead of just purely turn based, like fallout was.
Not all of those are criticisms, they're just ways in which the game is more similar to oblivion, technically a completely unrelated game, than it is to fallout 1 + 2, its predecessors. I know a few are nitpicking too, but once again i'm not trying to point out whats wrong with it, just why it doesn't feel like fallout anymore.
[EDIT] Oh and any of these i haven't mentioned:
Same engine, same levelling structure, similar (iffy) inventory systems, same voice actors, same quest structure, similar melee combat system, the default controls are practically identical, merchant system is similar.
They have a lot in common.