I never played Morrowind so Oblivion was my first encounter with TES series. I was blown away! World was lush, alchemy was a total trip. Fair enough the dungeons were a bit repetitive but what the fuck, there were a million of them? I did eventually give up on it on PC cos of the "1 crash per 30 secs of gameplay" issue but I grabbed a copy for PS3 and it was a lot better. I just hope I don't feel like you guys when I get my hands on skyrim and it turns out to be dumbed down and shite 
Well Oblivion was dumbed down in some pointless idiotic ways. In Morrowind you had long swords, short swords, maces, axes and spears for combat. In Oblivion? Axes and swords, spears were cut out of the game completely. Now, the funny thing was that the fusion of maces and axes was justified in game, as they both require a similar technique. But by fusing sword swords and swords, that implies that a thief skilled with a slender dagger will somehow know how to effectively use a claymore. Then the sense of exploration was totally eradicated by quick travel... Which Morrowind had, you just couldn't use it all the time and it wouldn't take you anywhere. With Oblivion? Any fuckass can teleport anywhere for no reasons, and there isn't even an interesting place to explore should you choose to totally ignore quick travel.
So, the only way they can dumb Skywim down anymore is if they were to fuse every weapon and armour skill together into some thing called Combat, and let you teleport onto
any spot of the map. Oh and have a compass that was akin to Fable 2's idiotic glowing trails. But there is some hope.. although, Skyrim is cutting down combat skills to one handed and two handed, but really? The RPG experience isn't about numbers and the manipulation of them, its about the experience, the world and the immersion.
That is why Oblivion utterly failed as an RPG, to me at least. But who knows, if everything they've hinted at about Skyrim is true then it could be fantastic.