As cool as the music is, it's simple and repetetive, and after 10 hours of gameplay, it gets more than a bit boring. If you are a metalhead, however, I doubt you'll mind much.

Should I get this game?
-If you can get into a seriously high quallity, Doom-esque FPS, absolutely. You must play this game.
-If your idea of a good game is a simple, gameplay driven, no nonsense game, buy this game.
-If you want to play a game with a well written story, a deep and immersive narrative, and complex characters, don't play this game. Honestly, if that's what you want in a game, watch a movie instead, maybe try out anime, if you haven't yet.
-If you truly hate metal music, and for some reason you refuse to turn mute the game, steer clear of this game, cause that shiz be blastin', my friend.

Overall rating = 7/10 (Pretty Darn Good)

Negative Aspects:
The story is really cheesy, but extremely I suppose that's just because of how intense it is. If you like action movies, you'll ♥♥♥♥♥♥♥ love the story of this game. The plot is basically about one man who fights his way through the army of hell single handedly to kill satan and be reunited with his girlfriend. It's horribly silly, and quite unoriginal, but it sure is ♥♥♥♥♥♥♥ cool.
The game can also be frustrating for a completionist player. I think I had to take a break or two while playing this game, due to how challenging it could be to complete some of the more frustrating, special challenges. If you don't care about that extra stuff, however, you probably won't run into any frustration, and if you're the type of player who wants a Dark Souls level of masochistic gameplay, then you'll have to look somewhere else, you weirdo.

I don't often find myself rocking out to a 20 second, royalty free metal riff on loop, but I do so consistently while playing this game.
I should also mention how impressive the game's engine is, especially for it's time. The levels are vast, the enemies are many, and I got it to run smoothly at 260fps in full HD with all the graphics settings maxed. It should be able to run pretty well on almost any system. Additionally, I can't say I can think of a single glitch I ran into the whole game. Oh wait, actually there were two. One time, I couldn't pick up a health thingy (which didn't happen when I replayed the level), and another time I messed up a level by jumping over what I assumed was the trigger point for the next event in the level, but I kind of knew I was cheating. That's it, though.
In summation, I F**KING LOVE THE GAMEPLAY. ♥♥♥♥♥♥♥♥♥♥♥♥'S GOOD.

Additionally, there are a modestly wide range of weapons available, each with unique function and their own fun quarks. Sometimes, it feels hard to choose which weapon to use.
I highly praise Painkiller not only it's extremely fun gameplay, but also the insane abundance of it. I never expected to get 30 hours of gameplay out of a single play-through of this game. I am a bit of a completionist, but with all of the collectibles/unlockables that this game has to offer, the length of this game could range anywhere between 10 and 30 hours, depending on your playstyle. If you want to dash through this game, as the pace of the game may have you inclined, you can, and I promise it'll be a blast.
The atmosphere is very solid and can, at times, be pretty creepy, even a bit scary. On the hardest difficulty, I found myself even a bit terrified at times. However, every battle is accompanied by the sickest metal loops this planet has to offer.

I just wrote a review for Painkiller: Black Edition, but for some reason, Steam thinks I've played "0 minutes" of the game and won't let me post a review for it. So, until I figure that out, I'll just post it here:

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Painkiller: Black Edition is a high octane first-person shooter that offers an extremely entertaining gameplay experience, especially for fans of classic shooters like Quake, Serious Sam, or Doom. Now, let's break it down.

Positive Aspects:
This game is a great example of a game that keeps you playing with it's gameplay alone, and none (or, in this case, very little) of the unlockable/level-up ♥♥♥♥♥♥♥♥ that drives most of today's mainstream games. It's fast paced, Quake-esque gameplay was thoroughly entertaining, and was made unique by the emphasis on killing absurd numbers of enemies. Your rack up thousands of kills just by playing the main story one time, and each level has totally unique monsters.