I think it′s a very good RPG. Building your own character the way you want it, and doing what you want when you want to.
See, that's the thing. Quite often I can't do what I'd like to do.
Morwen wasn't able to side with the Anvil Sirens even though she would have prefered to do so. She also wasn't given the option to cancel the Mages Guild's ban on necromancy once she became Archmage. During the later stages of the DB qustline Ra'Viir figured out that something was wrong (he found certain clothes in a certain house) but the game didn't let him do anything about it. In the finale of the FG questline Gilbert wasn't able to inform the Imperial Legion and let them handle the situation lawfully. Instead he was only given the choice of either being a vigilante and breaking the law or not doing the quest and neither of the options was in line with his personality.
Those are just a few examples. A typical quest in Oblivion only has one solution and the only choice you get to make is whether or not you want to do the quest in the first place. There are some exceptions (I especially liked the holy fire quest from the Shivering Isles MQ), but for the most part that's how it works. And that for me is the mark of a bad RPG. Oblivion as a game makes up for it with it's sandbox adventuring, which is okay in vanilla and good once you fix the level scaling, but that only qualifies it as an okay or good adventure game.
So I guess we'll just have to agree to disagree on this.