Made for FPS fans, not RPG fans.
Oblivion gets a lot of praise for it great storyline and fantastic setting, something I really can't understand. The storyline is simple, and the world is your run-of-the-mill fantasy world that's been invaded by demons. And there's really no atmosphere what so ever in the game.
The NPCs are very generic and very few of them are memorable. The interaction with them is even worse. You very rarely get dialogue options that will change the outcome of the conversation. You're pretty much just pressing "next" all the time.
The same goes for quests. One of the most important things in RPGs is having options, allowing the player to complete quests in different ways. You can forget that in Oblivion. If the quest object is to "get rid of someone", you are going to have to kill that person. If you don't want to do it.. Well, that quest is going to be stuck in your quest log forever. That's right, all quests are automatically accepted, and you can't remove them from your quest log.
What bothers me even more is all these Halo/CS/Quake fans calling this "the best RPG ever". But then again, Bethesda made this game for FPS fans and not RPG fans. The RPG elements are very simplified and dumbed down compared to classic RPGs, and focus is on the battles, not on building your character for the battles. One thing that makes this more evident is the level scaling. You can pretty much complete every quest at level 1 (with the exception of some quests that have level requirements), because the NPCs adjust to your level. No need to play it as a roleplaying game at all, just treat it like any other FPS.
All in all, it's a decent FPS game, but a horrible RPG.