Ah, I see, you were referring to the placing of things that would generally be consider clutter rather than the rooms themselves. That's fair. Even considering that though, thematically, Morrowind only had a number of flavors when it came to dungeons.
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Well see, here's my thing: I've got no problem with the limitation and repetition of flavors; it's actually a good thing IMO that dungeons should have some common theme linking them together so the player can begin to learn what to expect within that theme. And while I'm always game for more themes, I don't fault Oblivion for having limits in what themes it presents.
What I fault Oblivion for is in taking the vast majority of their theme-related clutter and non-room statics, pre-constructing it in the warehouse cells, and then directly copy-pasting the literally-exact-same theme-conglomerations where they fit.
To do an off-the-head comparison...
In Oblivion's caves, I could usually expect to see quite often that little cave-room with the table w/ coins and the plates, and the sacks of grain and torn-up crates across from the opening, the chest below the hole in the ceiling w/ light streaming down, and the bedroll tucked away in the corner. It was literally the exact same room, with the exact same stuff in the exact same positions, copy-pasted over and again. Or, in conjurer's dungeons, there were always the stone slabs, which always had the hourglasses and crystal balls and novice alchemy equipment on them. Again, exact same stuff, exact same positions. And these kind of things (of which there are a lot, even in the precise ways the roots grow out of the ceiling in a LOT of caves) add up to where the dungeon experience is full of direct apples-to-apples deja-vu. Except it's not just a feeling I've seen it before, it's a direct remembrance of "this entire dungeon piece, not just the sum of its elements, has been presented to me elsewhere."
In Morrowind's 6th house bases, you were always guaranteed the 6th house bells, the shrines, the tapestries, the corprus meat (yuck), the big stone tub-like repositories that held all the nice shinies for the dungeon, etc, etc. And that's OK, I would expect to almost always find that kind of stuff there. But where they were in relation to each other in the dungeon was different. What the dungeon had in variance of amount and variance of placement was different. Some dungeons had a crap-ton of those ash-statues, maybe all tucked in their container-pedestals in the shrine-room. Some had just a handful. Some had corprus-meat everywhere. Some had it only on ceremonial plates. Some put all their corprus where the treasure would've normally gone. No two 6th house bases, that I can recall, had noticeably copied clutter-environments. Or, to put it differently, there was enough uniqueness and change in the minute details, on a scale that was small enough, to offset any copy-pasting that was done in those dungeons.
I am so tired about people lying to themselves saying morrowinds dunegeons were better...no they were not... they had only a few different types just like oblivion with a few differences in each one. one thing above all the dungeons had no personality tho in morrowind. at least in oblivion they had a little. morrowind had ugly ugly caves full of nix hounds... mines...full of kawama... drewer ruins full of robots, daedric ruins, and shrines. but they all looked pretty much the same. no drewer ruin was that much different from another.
Perhaps we were looking at different things when we looked for what it meant to be a 'better' dungeon.
Morrowind's dungeons always had enough quirks and little design choices that conveyed its own unique story separate from any other story. They begged me to investigate what was going on beneath the surface of the obvious "oh, it's a [X-type] dungeon infested with [Y-type] monsters of size [Z]. And that investigation was made possible through the little things the designers tweaked throughout the level. When you don't copy-paste parts of dungeons into existence, you have to come up with some form of design-ideal to justify why some clutter goes where and why other clutter doesn't. In other words, the dungeon has an inherent account for why it is EXACTLY the way it is, on a scale that is much less discrete than simply repeating piece-conglomerations.
That is what Morrowind's dungeons offered me that Oblivion's dungeons lacked. As mt_pelion has said, FO3 has revived this facet of the game, to my happiness.