The "goth" kids. The DB in Oblivion wasn't very gothic as far as I can tell
Some people seem to think that any sort of "dark" character is automatically "goth" or "emo", really, the Dark Brotherhood members never really struck me as that. In fact, some of them seemed like they'd be pretty nice people if it weren't for the fact that they were part of a guild whose entire purpose in existence is to kill people, minus the orc who makes it pretty clear that he takes great pleasure in killing people, of course, that guy is clearly not right in the head. Okay, maybe Lucien Lechance kind of qualifies, I mean, just listen to what he has to say about the Night Mother, when you talk about svckling malice and pain from the Night Mother''s briast, even if only metaphorically, you have problems.
What Steve the Pirate said for what he wants is supposed to be what the DB are like. The Cyrodiilic chapter of the DB was horrifically cliche in the whole psychotic assassins department, it ended up going way pass the point of funny.
If anything, I'd argue that the generic cold, quiet assassin thing that we can presume the Dark Brotherhood was like in past games (I never joined them in Daggerfall though so I'm not sure what it's actually like, but in Morrowind the writing clearly says we're supposed to believe they're like that.) is cliche, while we've certainly seen psychotic murderous cults before, actually letting the player become part of one is pretty unusual. On the other hand, when have you ever seen an assassin in fiction that isn't calm, quick and to the point? That's pretty much the model of a cliche take on assassins, the Oblivion Dark Brotherhood actually struck me as reletively original as far as assassin's guilds go, whether it was a good idea or not is another matter, but I have to give them points for breaking from the norm, something Oblivion didn't do with its other factions (The Fighters Guild, for example, was pretty much exactly what it sounds like, and became boring as a result.) The Dark Brotherhood was my favorite faction questline in Oblivion. My main problem here is that there's not really any middle ground between being the noble knightly sort and joining the guild of murderous psychopaths, even the Thieves Guild didn't fulfill that because they were more of a Robin Hood sort, so while they're certainly illegal, it's debatable whether they really satisfy the less noble characters. There should be more room for middle ground between being a saint and a complete monster, and awkwardly wavering between the two doesn't count.
Also, aside from the orc, the Dark Brotherhood hardly struck me as inefficient, in fact, the contracts are always encouraging the player to use subtlety. The members may take pleasure in killing people, but most of them have the sense to do it in an effcient way when it's needed... most of them.
And since we're talking about assassin's guilds, I might as well give my thoughts on the Morag Tong, simply put, their boring. It's not the concept of the Morag Tong that I dislike, the idea of a legal, "honorable" assassin's guild that doesn't use subtlety because it doesn't need to is pretty unusual, but that very aspect that sets the guild apart from similar factions in other settings is what makes it so boring to actually do the quests, there's no need for stealth and subtlety, just walk up to your target, and kill him, if you have the writ, there will be no problem with the law, and walking up to someone and killing him is something you can do in any faction, a guild whose quests are modeled around it doesn't make for an interesting faction to be a part of on its own. Usually, the appeal of being an assassin in a game comes from needing to rely on stealth to kill people, and potentially needing to do so in creative fashions, it's about finding the most efficient, most effective way to kill someone possible, the entire concept of the Morag Tong ruined the appeal of a guild of assassins, yet if the Morag Tong returned but that aspect of them were removed, then there would really be nothing meaningful seperating them from the Dark Brotherhood. In short, the Morag Tong is the sort of idea that probably sounds interesting on paper, but doesn't actually make for fun gameplay.