The only thing in this game that feels like a significant step-back for me is dialogue. I loved having your skills open up dialogue options. It was one of those things in an RPG that made sense and added a layer of depth. Sometimes complexity is there only for complexities sake, but the old dialogue system wasn't like that.
In other ways, the game is way more advanced. Settlement building and crafting are huge additions.
Overall, I don't think this was such a monumental shift. TES had huge shifts from Daggerfall to Morrowind and from Morrowind to Oblivion. Many of us who loved Morrowind had a tough pill to swallow with vanilla Oblivion. I don't think FO3/NV to FO4 is anything like that.