I bought Painkiller when it first came out. If you like classic FPS Doom-style gaming then you'll love Painkiller: Black Edition. Like the FPS games of old, there is little if any story to the game. The story is only there to give you an excuse as to why the game exists.
Gameplay is simple. Pick up a weapon, get lots of ammo, and move forward into the next room. In the next room, you're locked in and you have to fight off waves of bad guys. Some areas are more open than other areas but the premise for basically every level is the same. If you're familiar with Doom, Duke Nukem, or Serious Sam then you know how to play Painkiller. The visuals in this game are gorgeous and even today they don't look bad at all. There is also a very basic multiplayer mode included.
I found Painkiller to be a refreshing break from the constant flow of girtty war shooters like Call of Duty, intense multiplayer games like Battlefield, and story-driven games like Bioshock. I also find it to be a good stress reliever - if you're having a stressful day, just load up Painkiller and blast away at the multitude of bad guys. For $9.99 you can't go wrong.