Oh boy! Do I remember my moments spent playing Painkiller with fondness. The best way to describe it, would be to say that it's a shooter distilled to be, well, pure shooting fun. The pace and the underlining music, as well as the fact that the game just *feels* solid and fun, make this the perfect shooter to pick up from time to time, have fun for an hour or more and come back to it in a few days, still enjoying the gameplay.
I like the fact that Painkiller doesn't pretend to be anything else rather than an old school arcade shooter in the heritage of Quake, and like the latter, the story is just a pretext to blow up, slice in two and/or nail the bad guys to the wall.
If like shooters without too much story depth and if you prefer a more toned down palette and a darker style, compared to the Serious Sam games, then you'll find Painkiller delightful, and since this is the original game bundled with the expansion, you should jump right on the occasion, as Painkiller Black edition gives you a lot of bang for the buck!