Far from brutal and not yet a legend.
I want to start with my love for metal. Metal is about harsh violent music and ecocentric philosophy, something to keep and experience for yourself, and big money games don't rhyme with it. Brutal legend is a commercial game with commercial rock/metal music and Jack Black might gives it a bit of fun and personality, but not enough. It's predicable, easy and redondant. The game is relatively short, so you might wanna play it again for achievements, but that would be the only reasonable reason, after finding the 200+ collectables that don't give anything much once you've finished the game. The storyline is straight forward and without surprise. The factions are interesting and worth a try online, but the gameplay is... well... you like it or not. I didn't. I was expecting a hack & slash style game but got a more rts-like game, which could had been a great addition, but too much is like not enough. The last quarter of the game is only about rts and you miss the brutal no-brainer fighting, a lot more if you're on a console.
I won't recommend it, but trying it ain't a crime. If you like it super, but it ain't metal.