I echo both trains of thought. Knights of the nine was probably my second favorite quest line behind the Dark Brotherhood. It has a good story and structure, and also has a good payoff with the last fight. It's an even better quest line if you're playing a Paladin character. The armor and weapons are awesome, and can even scale as you level if you put them back on the shrine, unlike other quest items that stay crappy if you get them early.
Also in agreement on Shivering Isles, wasn't big on it. It's a nice change of pace to occasionally step in for different scenery, but it was just...there otherwise, nothing special. After I bought it I took my Marksman through, and went back to normal Oblivion after I reached the city. Nothing held my attention, the land had too many high rises and dips (coupled with no horse) making travel akward. Instead of the cities feeling like cities due to a seemingly normal population going about their lives, it felt like they just gave everyone a psychological problem and tossed them altogether. Don't even get me started on the main quest. I finished the main quest in vanilla Oblivion and wasn't a fan of it, but have tried, and failed to get interested in the Shivering Isles quest. I can't seem to care enough to get past the drug addict painter dark elf. Much like most of Shivering Isles it's disjointed and not terribly interesting.
I realize I came down harsh on Shivering Isles. It's not horrible, but not compelling or polished either. It's not like it's the worst thing I bought DLC wise off the Playstation Network (that honor goes to that Capcom pirate Age of Booty game), and I did get use from it such as the new armor and weapons. I also give Bethseda credit for redoing the setting rather than just copy+pasting another forrest. However I also felt it was more of a distraction to break things up in Oblivion rather than something I'd want to play on it's own for any long length of time.
or killing some one I probably should not have.
