Welcome to W4O ;)
I really can't say what happened before Daggerfall as I don't remember being on or near the forums much then, but I can tell you it was very similar just prior to Morrowind being released.
I think both camps do know that Oblivion is a noteworthy game, otherwise why would they bother visiting the forums at all?
This is kind of what I think (and I could be completely wrong.. just how I see it.)
I believe the division in thinking is due, in part, to how they perceive the game and its development. The accepters realize that while the fanbase may have much needed input in the project very early on in its development, the developers are ultimately the ones that need to make the game work. Bethesda has a proven track record with the series of making enjoyable RPG's. They trust that this will continue and eagerly await the game. They also are not people who are quick to judge something until all the facts are in and they themselves have played it. Ultimately I think this group will enjoy the game immensely because they are not really looking for the negatives.
The rejecters on the otherhand.. I see them as having great expectations early on of their perfect game and are disappointed when the finished project looks less and less like it. They tend to dwell on these disappointments so much that they start forgetting the great things about the game. They also believe that if they scream loud enough that they will effect a change with the developers and maybe get it corrected back toward their vision. This, however, is never going to be the case. I don't think many of them understand that decisions to leave out certain features and add others are not just made lightly. The game has to function as well as be fun.
I think Oblivion is unique in the series for creating the raw hatred between PC fans and XBox 360 fans... that is all new. Since Morrowind definately was developed for the PC first and ported to the xbox late in development cycle.
Also I think nostalgia plays a huge role for many. Those that played Daggerfall and loved it wanted Morrowind to be an exact copy of the feelings those players got from Daggerfall. Many of them said they were disappointed with Morrowind because of the changes. Take me for instance... I was disappointed by the lack of climbing in Morrowind. I loved scaling the city walls at night to enter a city. When Morrowind was finally released I didnt miss it at all. It just wasn't needed in Morrowind. It will probably be the same for levitation... I will just wait and see.
Anyway... I notice I make longer posts when I am tired... I hope wasn't rambling too much..