As Shadowbeast pointed out, the forum tends to reflect a skewed sample of the gaming community. Most of the posters here are the "fanatics", as opposed to the "occasional" players who don't care enough to post here. Morrowind hit it big with the more avid fanbase, and is heavily represented here on the forums by the players who still play, or at least recall it fondly and are still following the series closely. Oblivion did better with the less-extreme or part-time gamers, who make up a large portion of the sales base (difficult to judge how large because fo their silence), but are under-represented here. Problem is, they're not as "reliable" a market for future releases as a dedicated following.
Morrowing had a better, more varied world. sure.
Oblivion had a lot better combat.
They both are about even on the quests relatively straight forward RPG stuff. Neither was particularly poor or great.
But what about character customization/control( from character creation, to spell creation, to enchanting).
Oblivion was much better.
And immersion graphics/sound/the ability of the game to make you feel like you are "there".
Oblivion wins here again IMO.
If the world is engaging /interactive enough, I don't care about quests. I'll go do my own thing.
OB had "more interactive" combat, and was "better" from a FPS perspective, but it didn't reflect the skills and abilities of the character as well as MW's system, so it was a "worse" RPG" combat system.
Character customization in OB was better from a visual perspective, but the heavy reduction in skills, and especially the "irrelevance" of skills like Security and Speechcraft (which were in effect "replaced" by mini-games and player skills), made it a lot less meaningful. That's not "better", just "different" at best.
Enchanting went from something that any character could do to a limited degree, but could become insanely powerful if you worked at it in MW, to something that "any barbarian" could do with equal ease to a trained Mage in OB, by using Sigil Stones. The types of enchantments went fom 3 (Cast on Use, Cast on Strike, and Constant Effect) down to 2 (no Cast on Use) in OB. Taking Enchantment as a skill in OB simply didn't pay, and my attempt at playing an Enchanter character came to a quick end as I realized that it was pointless. That again isn't my idea of "better".
Spell creation was easy in MW, all you had to do was pay a small fee to the proper Mages Guild member and you could have any spell tailored to your needs, regardless of level or class. Casting it was another story, and required something called "skill", and possibly another called "practice". How is OB's system better?
Morrowind made me feel like I was "there". Oblivion made me feel like I was "here", but with supernatural powers and Daedra running around. Better graphics, yes. Better sound, maybe. Cyrodiil was boring, though. The lack of "working" transportation, lack of farms that farmed (except for the nicely done area around Skingrad), the lack of mines that produced anything other than Goblins, and other such details left me feeling like it was the aftermath of a disaster that exterminated the population and left it in ruins, rather than the busy and industrious heart of a still-thriving Empire just past the height of its power.
The focus of the two games was totally different, and what one player likes about one and hates about the other is exactly what another player hates about the one and likes about the other. That's the downside of Bethesda's attempt to broaden the marketbase of the game by making it more FPS-like, at the expense of RPG play.