Well, what is a role playing game?
It's not just a game were you play a role. Else Call of Duty would also be a RPG (you play the role of a soldier).
So what is it then? Is it something like stat- and skillpoints? It it about creating 'builds'? Well, you can have 'builds' in all sorts of games. Even in RTS, shooters and even in some tower defense games. Sometimes it's called perks. But I don't think just having stats and skills makes a game a RPG.
To me a RPG is all about the story and how you have effect on that story. A real RPG should contain choices. So can you can 'develop' a story around your character. Do I join the bad guys or the good guys? Your playthrough should be different than the playthrough someone else does. You should get enough choices so you can play through your own story.
If we go back to Call of duty, according to my rule of RPG, call of duty is not a RPG. Because you can't make any choices that affect the story. Everything is linear and you can't change a thing.
If you take The Witcher as an example, this game is a RPG because you get some choices in the game that have consequences.
Skyrim wants to be a RPG, but it has no really important choices. Everyone is experiencing the same gameplay. You are a mage/fighter/thief/murderer at the same time. (With this I mean you can join almost ALL the guilds and clubs, even if they have conflicting values) Skyrim does have choices, but none of them are very important, so they don't change the story around your character. It's just an open world action game with fantasy stuff in it.