Is Dark Souls an RPG?

I love Dark Souls. It was sort of a sleeper hit for me, but it has become one of my favorite games of all time. I have posted a few times (back in the Verge days) about Dark Souls being an RPG and got some push back, saying that it isn't really an RPG and is just simply an Action game. The main argument I have seen is that it doesn't allow the player to take on the roll of a character and have an effect on the world. If this game doesn't do this then I don't know what I've played for 200+ hours. What do you think?