EDIT - Did you play pt3 Deep Blue too?
I am actually DL the series now. I never intalled the first part I got because Nexus was having trouble at the time I was going to DL the series. The question now, do I dare install it on my top heavy mod list.... END EDIT
Mmm, may I suggest Puce Moose Quest series.
They might be a bit twisty and hard to grasp but with a little help from his FAQ that works in a tree format to give away as little as possible in small clues, and help from the posts on Nexus you will do fine.
They might seem small and just a couple of quests but suddenly you notice you just keep continue finding stuff and doing new things, they are just amazing complex mods. So don't make the misstake thinking you reached the end just 'couse you have a couple of resolved finishes.
Linky to one of his mods http://www.nexusmods.com/fallout3/mods/6921/?
A note easily missed is his first and that is not that complex. His next, an evening with Mr Manchester just goes on and on, ha ha. And if you got Point Lookout, In the shadow of the Swamp is great. I just finished one part of the swamp and am back in the wasteland doing other things for the time being, maybe getting further in Mr Manchester.
Cheers!