Despite not finishing Dark Souls (or any other Souls game) I'm a huge fan of them. There is something just right about the atmosphere and the gameplay that I just have not found anywhere else. Ever since I played it most games felt... less fun as they all seem so simple and... so not rewarding.
But, indeed, more than the gameplay, I love the Souls series for the way the world is presented to you. No strings whatsoever and a world to explore. Open world, yes, but with a purpose. A wonderful (albeit deadly) world which is just so nice to be in. It has a sense of calm, of peace, disturbed by the enemies that stand in your way. It is also dark and dreadful when it must be. Sorrowful at times, too.
Sadly, it didn't hook me and make me want to play it until I was finished. Still, what little I played was... like seeing the what the future may hold for us. It was like walking into the world of a good book and being able to see it for the first time - most games don't manage to do this. I hope that it goes down as both as a classic, and a turning point. Despite the flaws the series may have, there is much for everyone else to learn from it, in my opinion.