Look, the word MMO is thrown around a lot these days as a buzzword, sometimes in the case of Destiny. Although it has MMO-like features, I wouldn't consider six-person squad-based shooter with a hub world an MMO. Similar to Diablo and Phantasy Star Online, they mostly lack that first M, "massive."
But I do like the genre-creep though, especially when it comes to the focus on high-end loot, endgame, and raids. Speaking to IGN, Bungie divulged a bit more information on the latter, noting that it will feature multiple mission types and not just singular boss fights like Borderlands traditionally features.
Apparently for raids, you cannot use matchmaking -- so players will have to hand-craft six-man squads (start recruiting now!). These raids will take a few hours to complete, and are "self-directed" challenges -- in other words, they won't have waymarkers or linear instructions.
They are designed to challenge players not only by way of skill, but also challenge your build and equipment. Yep, I'm all in on this. If Bungie can continue to add content weeks and months down the line like this, I'll be playing it for longer than the average RPG-shooter hybrid.
Also, provided that the DLC is done right (you know it's coming), it could cut down on the "one and done" mentality for story-based shooters. I hope that they're more like expansion packs.