But isn't a 3rd person game where you only control one person called an RPG. Even though it may not have a lot of talking situations to make it boring, it is still an RPG. Even if it is an action RPG, it is still an RPG. You kill things and pick up items to trade or sell.
RPG stands for Role-Playing game (or acually computer role-playing game, but you usually neglect the c), and a role-playing game is about experienceing a story and roleplaying. You neither experience a story nor roleplay in D2 => it's not a RPG. As simple as that.
And as a said, despite the name action-RPG's doesn't really have much with RPG's to do.
Übereil