My one-word summary: Unpleasant.
Visually - everything either looks like crap or the inside of a horrible airport hotel (ie, The Institute). FO3 at least had some style (the art deco/Metropolis-ish stuff etc etc).
Exploring & quests - apart from looking like crap, most of the interiors are...
The ArsTechnica review is the best I've seen so far.
Can't post a link?
Anyway: miserable pacing, boring NPCs, redundant, crafting/settlement stuff tedious & unrewarding, But some major story & atmosphere payoffs amongst all the glitchy stodge.