I did enjoy Oblivion on its own terms but compared to Daggerfall & Morrowind it is indeed completely ****. Maybe Bethesda will redeem themselves with TES V... FO3 was a step in the good direction for me.
Biggest problem is they completely messed up the lore... like the 'bad guy' misnaming all Daedric realms near the end of the main quest - which wasn't intentional but due to mistakes made by writers... would this had happened with Ted Peterson or Michael Kirkbride still around?
EDIT: Also what they did in Shivering Isles was greatly over-the-top... they turned lore topsy-turvy because they thought it would be fun (and indeed it was, becoming Mad God and what not), but I highly doubt they thought about the consequences of this on future Elder Scrolls games. In all Elder Scrolls games the previous hero 'disappeared', but when a hero becomes a 'god'... well....
Another example is the upcoming Elder Scrolls novels, where suddenly a flying city of undead & a new Prince appears out of nowhere... fun indeed.