As of this week Bulletstorm has been pulled from the Steam marketplace. Though there has been no statement from EA it is assumed that this is because of the GFWL servers shutting down in July of this year. More than likely it will come back to Steam with Steamworks instead or some variance in DRM (more than likely, this is EA we are talking about here) so don’t get your pitchforks out yet.
The game is still available on Origin if you must absolutely have it and if you do have the game you can grab your cd-key from Steam and it will still activate on Origin and place it in your game library there. I have talked to EA support multiple times in the last year asking about this game, as I absolutely loved it, and I was told each time not to worry and that they are working on the GFWL situation. Stay tuned.