About a decade and a half ago, when I was just getting interested in video game design, I said something. It was something along the lines of "The future of games is going to be a service model, its the only way to prevent piracy and milk money from a franchise without pissing off your customers."
I had been playing Everquest Online Adventures (the PS2 everquest release), also the space game Diaspora (a micro-mmo). I truly was fascinated by the genera, it was new, interesting, and seemed foolproof.
Blizzard learned that lesson too, after World of Warcraft, they stuck with the service model. Even starcraft 2 is essentially MMO architecture with a simulated single player game attached. Diablo 3 has taken it a step farther, not just MMO architecture, but everything is multiplayer, singleplayer is just a closed instance.
However, blizzard lost something, they forgot that a service needs to also not piss off your customers, you need to market the service, not the game. With an MMO, you are marketing a multiplayer game, a community. With Diablo 3, you are marketing... an auction house?
Traditionally Diablo 1 and 2 were singleplayer games, the people who love the game, largly, played it singleplayer. There certainly were many who played multiplayer (I was one of them) But I also played it singleplayer, or over LAN quite often. Infact, in the later days of Diablo 2, I only played modded variants over LAN or single player. I havn't touched battle.net in 6 years or more.
If you are going to make a game that is tied to a service... make the service first priority and the game second. Blizzard did not for starcraft 2, and it took them 8 months to fix battle.net 2... nor did they for diablo 3 and so the multiplayer aspect exists, is the center, but is a joke and since singleplayer is multiplayer without other players... it too is a joke.
In a few weeks or months i'm sure they will fix it, but if starcraft 2 is an example, it will take them a long time to get it right. (I quit sc2 after 5 months of waiting for them to fix the custom map interface code, I ONLY played custom maps, and created custom maps.)
Wow would be rubbish without the multiplayer, everquest would be rubbish without the multiplayer, Diaspora would have been rubbish without the multiplayer. Look at all the service games you play, and ask yourself how fun they would be without the service, without the other players, without community.
If your game is better with players than without, it deserves to be a service, if it would be better singleplayer than the crappy service code you shoved down the buyer's throats... then you should be kicked in the ass.
Multiplayer roguelikes are commonplace, they are a tried and true genera. They are NOT however a service, if you want them to be a service, you are going to have to rework the genera... blizzard failed.
I'll be playing torchlight 2 and possibly Path of Exile :p