I have played Fallout for 3 hours now (not a lot, but to get an impression)

It is basically 80% Oblivion and 20% Fallout.

No question, there are a lot of Fallout elements used
in this game, but they seem to be somehow "stuck into"
the Oblivion Idea.

The VATS system is nice.
But a real roundbased combat would be my favorite still.
(Knowing that the younger gamers would not like such complicated things)

These things I miss from fallout:

-Pictures of the items you have
-descriptions of the inventory items
(the items feel like made by a "mass production" template system, there is nothing funny about them anymore)

-The nice background tone (the fallout 2 music is way better)

-text descriptions of ambient items you select (they are great in fallout 1+2)

-the SPECIAL + Perks interface.
If they would have been "brave" they would have kept this original Menu-page 1:1
But the Menu with the new Pipboy is annoying, unhandy to controll and does not look nice. Its clearly a decision to make it work better on the game-console versions.

-The "vault feeling".
I think the beginning of fallout 3 is crap, and very staged.
The vault feels like a small, scripted Oblivion dungeon,
not lieke a huge underground society.
There is no "attachment" with the vault, as in Fallout 1,
where the vault dweller had to save the vault.
In fallout 3, the vault is composed of boring or annoying people, that
want to bore or kill the player. I would not mind to press a button to blow up
this thing, and leave it behind, there is nothing of any interest in this vault.
Fallout 1 and 2 made these areas feel much more like an "island of savety"

-random encounters with dialogs.
I was running around a bit, just meeting raiders and dogs that attack righ away,
not this cool thing when enountering a caravan and trading with them.

anyway, I dont think its a bad game.
But it is not a sequel of Fallout 1 + 2
(its much better than Fallout tactics and this BOS though!)
Its a good Oblivion based roleplaying game in an endtime setting.
(with some Fallout assets)