In response to the Dark Brotherhood & Thieves Guild quests, I found both to be somewhat watered down from their Oblivion counterparts, at least mission wise.
The Dark Brotherhood is much more... simple to put it bluntly. Get in, kill someone, do something extra for a bonus, leave. That's about it. I mostly backstabbed or sniped my targets and got every bonus rather easily. Also quite a few of them lacked a satisfying amount of stealth action, other than sneaking up behind your target or perhaps swiping something from a desk.
In Oblivion I struggled to kill some of the people, let alone obtain a bonus.
Thieves guild was similar, somewhat more action-based than I would have liked. For instance, one quest has you prowl through a dungeon fighting Draugrs and has little if any required stealth involved.
Those details aside, I did enjoy the storylines of both very much.