Shivering Isles rivals Morrowind in my mind. It has a strange and unique setting and most of the content is incredibly well-written, which contrasts sharply with the standard medieval setting of baseline Oblivion (mandatory reminder that Cyrodiil was supposed to be a rainforest, but the devs retconned it to make development easier).

The other expansion, Knights of the Nine, was just a bunch of fetch quests to unlock an armor set and was disappointing in comparison to even the base game (though at least the final boss fight was cool). It also put behavioral tracking on the DLC's rewards that would disable them if your character gained infamy, forcing you to repeat a bunch of boring travel quests to fix them whenever this happened. There's a reason KotN never comes up in discussions about the game.

[–] samus12345@lemm.ee 4 points 1 day ago* (last edited 21 hours ago)

Shivering Isles rivals Morrowind in my mind.

Same. It's easily my favorite Elder Scrolls expansion, period.

mandatory reminder that Cyrodiil was supposed to be a rainforest

I never knew that. Shame the devs for this didn't go for it, but I suppose fans would be up in arms about it.

EDIT: Apparently they actually DID add some rainforest-y looking locations!