Geez I must be playing "wrong..." I'm level 13, been playing over 30 hours, and I haven't even unlocked the specializations yet. I didn't even reach Skyhold until 25 hours in.
Either way, I'm playing a dual rogue, and my party is almost always a combination of Cassandra as tank, Solas and a spirit mage, and a second mage as pure DPS of whatever type would help the most for the area.
You unlock them at the war table. It's a mission called "Specializations for the Inquisitor". Also, best party setup in my opinion is two tanks (one templar and one champion), a mage (knight enchanter) and a rogue. You're champion and knight enchanter will basically never go down, and if you're templar goes down, you can have her speced in a direction which heals the whole party. At higher difficulties, it's the only way to go.
Bungie themselves call it a "shared world shooter". Calling it an MMO is about as accurate as calling Diablo 2 an MMO. You're just going to argue anything and everything. And I freaking love Destiny, but it's no doubt that game is flawed as hell.
It's good. You have the most awesome weapons in any AC game, and a likable protagonist. I felt it was kind of a more serious AC/Pirate-version of Django Unchained, but that probably just has more to do with the theme.