I disliked it because it basically wasn't the DB. They're just a bunch of assassins under the DB name, they don't follow the Five Tenets.
I realise the point is that the DB have become this, the last remaining sanctuary in Skyrim (seemingly Cyrodiil too, I think I read somewhere that the Listener was killed in the streets of Cheydinhal due to a riot.)
Reminds me of Final Fantasy X-2 really. Yuna because a free spirit in this game, wasn't held back by her 'duty' as a summoner, and I simply didn't enjoy it. Again it was the point but it doesn't justify it being remotely decent for me.
It was the last sanctuary not just in Skyrim but in Tamriel, at least that's what they say. I have a hard time seeing how that happened though, but I guess it's possible.
The one's in Cyrodiil were either destroyed by the Thalmor or riots, the sanctuaries in Elsweyr Valenwood and Summerset would obviously have been destroyed by the Thalmor earlier on. Morrowind never had one, the Black Marsh cut of contact with the outside world, and never seemed to have a sanctuary in the first place, just Shadowscales who were trained by assassins in Cyrodiil, which is obviously impossible now.
How the sanctuaries in High Rock and Hammerfell were destroyed however is beyond me, especially High Rock is difficult to explain. Still Bethesda wanted to tell a story of what would happen with the entire brotherhood destroyed and how you can return it, at least a bit to what it used to be. I don't really mind that.
The reason I like the DB in Skyrim more then in Oblivion comes from three things I guess.
1. You can actually be evil, in Oblivion the worst you did was kill all your own people, well great.
2. Here you actually kill innocent people and the freaking Emperor. It just has a far greater impact.
3. They don't worship Sithis, worshipping Sithis is insane, to the point of past insanity. Sithis equals nothing, how can you worship nothing. Not a force representing nothing actually a force of nothing... I don't get it.