Painkiller is in the same vein as Serious Sam, Duke Nukem and Doom. There's no physics puzzles, no epic story, no tactical choices. It's all testosterone and violence.
Painkiller swarms you with wave after wave of enemies, arms you to the teeth with a wide variety of wierd weapons (a gun that shoots shurikens and lightning) and tells you to get from point A to point B in one piece. That's it. There's a story here about demons and your dead wife or something but it's largely passable and is pretty much only used to establish the fact that you're killing demons.
Painkiller: Black comes with the original game and the expansion, Battle Out Of Hell. While the first game is excellent all around, featuring some really nice level design and trigger-happy gameplay, the expansions seem to fall flat on their face and really aren't worth touching. That said, it's still a pretty good steal to get Painkiller for ten bucks. This is a classic mindless shooter. You can't do much better.