Let's see, ignoring the Fallout part (still closer than 3) or the lack of RPG on it, the good compared to F3:
-Better difficulty. In F3 only deathclaws offered any danger, here enemies are thougher and more clever (a.k.a. less retarded). The "skill checks" are more difficult, with average CHA you aren't going to see much sucess, and you run into plenty of EXPERT locks quite early.
-Better gameworld. An illusion of real economy with farms and the like. Enemies don't seem so chaotic/evil/dumbfuck as before (most raider groups have a named leader and some basic backstory, even the SM feel less orcish now).
-Less good versus evil (haven't seen what's the Institute up to yet, can't be worse than F3 anyway). And the BOS seem to be closer to their original self, selfish but not as dicky as in NV.
-Writing *is* better (like that was difficult
), haven't found many derpderpderp moments so far. There is a stupid junky/diviner lady early on, and I've just met a scientist that seems to be a Moira knock-off.
...
It's good for what it is.