My two cents: Morrowind goes down as a personal gaming milestone. Never before or since have I gotten so engrossed in a game... I shutter to think how many hours I poured into it (on the old Xbox, no less).
Personally, I couldn't bear to play it again... it just doesn't age well.
My biggest complaint, both then and now, was the whole behind-the-scenes die rolls... that's not something that really belongs in a computer game, if you ask me. Pen & paper? Sure. :/
Oblivion was awesome, too. I won't deny I'm a sucker for pretty graphics, and IV certainly trounced III in that regard. Also, no die rolls was nice. Active blocking was cool, too... I didn't like that spears, medium armor, clothing slots and weapon classes had been removed/altered... but omitting these things streamlined production to some degree, I should think. That's less assets to fuss with for modelling, texturing, animations, etc etc. Less/consolidated skills means less under-the-hood calculations to slow things down, too...
I still don't necessarily like the fact that this trend has taken over Bethesda games (and BioWare, too), but these sacrifices could very well lead to more stable games... just random, baseless speculation on my part, though. >.>