Has been confirmed. There will be two new bosses, superior graphics and gamepad suppourt. Otherwise, the game will be unchanged. The release date is August this year. If you didn't know, Dark Souls is a fantastic dungeon crawling action RPG. It even got a few GOTY awards from large publications. The combat system is deep, visceral and satisfying. The story insignificant but creates mystery and tension. The multiplayer features are excellent. But the main draw of the game is its brutal difficulty. You will die many, many times in this game, there's no avoiding that. But in my opinion, the euphoria you experience after beating a particularly tough boss is one of the best feelings you can have from gaming. It's epic, challenging and compelling. It's also console exclusive (despite how it being a dark and hardcore RPG), but a fan petition has changed that. It's nice to see companies increasing their commitment to PC these days, especially in response to fan demand.
The real question is: is this game good enough to counteract the fact that it uses Games for Windows Live?
For the existing content, no. There will be an entirely new chapter called "Artorias of the Abyss" which will feature three of four new bosses and as many new areas, and a refined PvP mode.