Yeah, ignoring UI issues and some tech issues that I've gone over ad nauseum FO4 certainly did raise the bar quite a bit otherwise, but I wouldn't call them innovations. They're iterative improvements on what we've seen before in previous Bethesda games, which in turn tends to be things modders added in previous games. Building homes and such was fairly quickly modded into the games, so Skyrim got a DLC for it, which in turn became a full thing in FO4.
As for roleplaying opportunities, they actually lowered them compared to previous outings. I'm a bit disappointed by the way they handled factions and how to interact with them, and how interacting with them affects how you deal with other factions. Followers reacting a bit to what you do is a good thing, but not innovative either as that happened already back in the previous Fallout outings.
One thing they did make all new (as far as I know) is how interior cells now interact with exterior cells. If it rains or there's a radstorm or something in an outside cell, and you're in an interior cell in that area, rain and thunder and even lightning flashes will occur in the interior cell as well. It'll even rain through holes in the roofs etc. You can even hear combat going on outside (or inside if you're outside) if NPCs are going at it near you. I'm not sure how much work that took, getting that ancient and endlessly hacked together engine to do these things, but I'm impressed. It's one of those little touches that takes a lot of work, and aren't at all necessary but just makes you nod in appreciation with a little smile as radstorms practically shake the building you're inside.
There's even rain occlusion in the exterior cells, letting roofs keep the rain off. Just a little pity the "you're wet because rain" shader still applies.
The various fog and environmental effects are also top notch. It's remarkable how much every area can change immensely based on the weather you're in. I haven't seen confirmation of it yet, but I've also heard there's an actual weather system in place where various weather (storms, fog, radstorms, rain, etc) actually moves across the map in patterns. Radstorms for instance supposedly are "born" in the Glowing Sea and move outwards throughout the Boston Wastelands. Take that as the rumor it is, until you see confirmation somewhere, but in my experience it might very well be true.
Edit: I am slightly miffed by the performance impact of some effects in urban areas. Go into the cities when there's some fog and god rays and you can see a steady framerate-locked 60 go all the way down to 30, depending on what you're facing. And this is with a gaming system that's pretty much top of the line. The game doesn't look -that- good that it justifies 30 or below on systems like mine. It seems to be well optimized most of the time, but these... less impressive bits are a bit vexing.