After 10 hours, I began to experience all the bad things about the game, yes.
In 10 hours....in a time which allows you to barely complete the MQ (1st playthough)...yeeeah.
I then later tried it with OOO+100 mods, but seriously even mods can't fix this game.
Neither with all the tons of excellent RP-oriented mods that there are out there? And the dozens of awesome questmods? And new items? Of course, it'd take much more than just 10 hours only to see them all...
Yes, all quests were bad. Even the Dark Brotherhood quests, which are hailed as the best, are still pretty bland, although slightly better than the rest.
Let's technically "agree" on that (which I don't), but...
Saying "roleplaying is entirely up to you" is pretty [censored], no offense. I had no choice on how to play my character in the game through my choices and those consequenses
...you've freedom of choice since the very beginning. I've roleplayed without problems an assasin/thug/skooma dealer, a paladin/knight/Imperial Legion officer with a big castle and men to command, and a mad mage who had his lair in a pocket dimension, along with unique quests suited for all of them.
Vanilla Oblivion was not perfect indeed, but still a good game to start with. But saying that "neither mods can save it" is being utterly and totally ignorant, and thus your arguments are pointless. Also, having played
only 10 hours contributes to that. RPG's may not be your gaming style (in fact I'm sure they aren't), but don't blame them for that.
If all dungeons are so terribly repetitive, then yes, they are indeed bad.
There's a difference between repetitive, and bad. Learn it.