ok, it was really awesome.. MOST of it, not all.
i thought that first part where all the trolls come, then you somehow appear right over a hole, and then fall some 3 km at over 1000 km/h to be quite silly. And then you fall at that speed over some thick wood and you survive. Yeah right.
aside that and the Underworld Train, I think all the rest of the Underworld is a LESSON to Bethesda on how to do dungeons.
in fact, Nehrin has PLENTY of epic dungeons and locations, you know, with a sense of magic, of grandeur, of fantastic and fantasy. None to be seen on Oblivion. The real medieval europe had more impressive buildings and locations than the Elder Scrolls Series.