I think it's kind of misnomer to call Skyrim a great RPG. From a mechanical perspective, Skyrim's leveling system is really bare bones, and the Dragonborn never gets the opportunity to characterize themselves.
Compared to the truly elite RPG's, (KOTOR II, DA: Origins, Mass Effect 3, Persona 4, IMHO) Skyrim doesn't have a lot of, well, role playing.
But none of that matters because Skyrim does something else better than almost any game I've played; it offers a sense of discovery. You become invested in Skyrim's setting and characters not because it has a fantastic story or deep gameplay, but because Skyrim makes you feel like the adventure you go on is truly your own. This works because there is nary an inch of Skyrim that doesn't demand exploration and examination, you always have something to do, and what you do is almost entirely up to you.
Because you can wander Skyrim so free of distraction or breaks in immersion, because the game almost never throws up invisible walls, it becomes more than the sum of it's parts; you start to feel like you could actually live there.
Bethesda are not much for stories or complex game mechanics, but they are masters of setting; Skyrim is not much of an RPG, but it's one hell of an open world game.
We've come to define an "RPG" as a game where you have a level and you get stronger, but like many of our genres, this idea misses the point, because it doesn't express the underlying appeal of Role Playing.
World of Warcraft and Planescape: Torment are both "Role Playing Games", but the sources of their appeal could not be more different; most of our genres are arbitrary distinctions.
Maybe I'll dream up some more fitting names one of these days.