Not fond of them in Skyrim.
1/Oh what a surprise - you turn out to be the listener. It's apparently now impossible to join a guild without ending up running it five minutes later. Personally I think it would have been far more interesting if you had to find the new listener and help them establish themselves. I'm sick of being boss of everything in this game. Can't Bethesda think of handling guilds any differently these days? Has their imagination totally run dry?
2/Characters are very one dimensional except Cicero who's annoying and Astrid who's made inconsistent (see below).
3/Opening quest is arguably the dumbest is RPG history. I really wish there was an option to drag Arentino back that orphanage where he belongs. The Jarl has, after all, ordered him to go there. But apparently the city guards can't handle a small child.
4/Usual nonsensical plotting
Spoiler Like why would Astrid be so dumb as to believe by betraying you the rest would get left alone? And I thought this job was tremendously important and the brotherhood's big chance to make it big. Why not just say "Ok guys they're onto us - time to move to a new hideout". Astrid is supposed to be clever, cunning and a bit paranoid, yet she suddenly behaves like a totally naive idiot [/spolier]
Still, nowhere near as badly written as some of the other questlines and at least they do manage to keep the quest about assassinating people - unlike the thieves guild and Hogwarts where you can just hack and slash your way through supposedly magic and thieving based questlines.
5/Making it too easy
[spoiler] Like the way you can walk up to that guy touring the cities, tell him you're going to kill him and then he attacks you letting you blatantly murder him with no penalty. You should be forced to stealth kill him like the assassin you're supposed to be. It's perfectly doable. Not to mention you can just blatantly kill Grelod in front of everyone
6/Gimp suits. Having a specific armour set for secret assassins is a dumb idea in the first place, making it into a totally incongruous gimp suit is ridiculous
7/Usual thing of you can't play the game for more than a couple of hours without having the quest dangled in your face. It would have been really nice if someone as secretive as the DB were someone you stumbled on. Oblivion had an imperfect but far better way of introducing them.
Depressingly, I reckon it's still probably the best of the guild questlines.
Edit - weird thing going on with spoiler tags....second closing one isn't showing, but I typed it in...