After Oblivion, Bethesda's games become sandbox themeparks where you can do a lot of stuff with little substance while chipping away any RPG mechanics.

I think Oblivion's success despite its shortcomings on the RPG side gave them the message that this works and Skyrim's success reinforced it even further.

Though personally i find Morrowind the best of their games by far, especially on the writing side (not a surprise considering the writers they had - and lost right after Morrowind). Not as chaotic and repetitive as Daggerfall and Arena's random generator-based worlds, yet still with solid RPG mechanics, writing and exploration.