The best they made, for me, was Morrowind.
While I enjoyed the rest of entries and I’m very fond of the Shivering Isles, IMO it was the originality of it, its story and art, but also the freedom it granted.
My advice would be to go back to that time and instead of massive places, just build a fun place to explore.
I remember well going for a quest, seeing a cave and then falling through a rabbit hole into a death cult while being a laughably underpowered magician.
It felt closer to what I commonly experience with D&D than other games, mostly due to the combination of freedom and curated world.
That said, yes combat was dull, uninspired and probably the weakest part of the series.