The "M" rating pissed me off. Took like 2 years to convince my mom there was nothing wrong with it, that some [censored] modder put nudity in it. If you want nudity go buy a [censored] pormo.
The M rating was not for modded content. A game designer cannot be held responsible for what an end-user inserts into their games.
The nudity was an unused bare upper body mesh file that Bethesda did not delete and shipped with the game. However, that unused mesh files was not the reason that the game changed to M. The unused mesh simply prompted the ESRB to reevaluate the game, and they discovered that the amount of blood, gore, and graphic architectural design, was far more intense than what Bethesda had shown them. Oblivion has an M rating for gore.
I mean, look at the Deadlands. There are containers made out of stretched flesh, or of twisted red still-pulsing tissue. The floors and mezzanine of the Sigillum Sanguis was made from sewn muscle. There is blood or bloodstains on pretty much everything. It is horrific design.
Or in Arkved's tower, where you can find yourself surrounded by hanging corpses on all sides. And on the subject of corpses, their meshes are incredibly detailed in terms of decomposition and gory detail.
Oblivion's design choices deserved an M.