For me, the best open-world games were Gothic 1 and 2. I haven't played Skyrim yet, but Oblivion was ugly, consolised and dumbed down. The characters did not do anything, while in gothic they slept, forged weapons, talked to each other, even shouted at you when you trespassed. In Oblivion you can pick a house clean and the guy is still smiling at you.
Morrowind killed the fun by having stupid combat system - "always use best attack" was in options, that is what you call "system"?
RPGs would be worth playing if they had combat system like Mount and Blade. The story usually makes for it -and I loved Dragon Age, but the main game mechanics is running around and killing things by stupid mashing. Boring.