You can make a custom character - RPG Element
You can make choices - RPG Element
You level up Skills - RPG Element
You can choose Factions, Religion, Moral and Personality for your character - RPG Element
You choose Abilities and Talents (Perks) based in your Skills and "Class" - RPG Element
You can roleplay many different roles - RPG Element
It isn't, for the most part, linear - Open-World RPG Element
For a game that isn't a RPG... It really looks like one.
If anything it's more a Live-Action Roleplay and less a Pen-And-Paper Roleplay.
The Bosmer NPC Gwilin in Ivarstead has a wonderful quote about the game. I'm going to copy it for you.