I've yet to actually finish Oblivion, but a couple times a year I'll restart playing and do so for about 1-3 weeks of casual play and the next time I feel like playing I'll re-start with a new cahracter again. I see it as a good overall package that does everything a CRPG should do fairly well but there are enough games that overshadow it in specific areas that I see it as an example of unrealized potential.
I felt morrowind was a much more immersive gameplay experience and that one held my attention from start to finish. The thing about morrowind that I realy thought was well done was the storylines and quests for the various factions and guilds. In oblivion, the thieves and fighters quests were just meh kinda boring to me, but I did like the mage guild questline and the dark brotherhood was reasonably good, but I was very disapointed in its ending. The overall darker atmosphere of the game was preferable to me as well, but thats more of a personal preference than anything else.
What I'd reallllly like to see tho is a remake of Daggerfall wilth modern graphics and a lot less bugs. The behind the scenes faction stuff was amazing in theory, but with how buggy the game was, I don't know how much of it actually worked as intended. Of all the TES games I've played it really felt the most like one where you could do whatever you want, but the actual plot part of it was too hard to get into because of all the bugs so I can't really compare it to Oblivion and Morrowind.
I never played Arena or Battlespire, so I don't know what I missed with those...