It's not a bad game at all, but Brutal Legend. For the simple lesson that, if you're going to give your game new, interesting, creative gameplay, you'd better damn well redouble your explanations and tutorials. Because it doesn't matter how well the mechanics fit together, or how fun it is when you play it right - if you can't get players on the same wavelength as you, they're going to think that the gameplay just plain sucks - as a lot of people did.
Which is why I think it's kind of sad how Double Fine put so much effort into designing Brutal Legend's stage battles to blend the action and strategy genres in a way that keeps the epic battles of RTS games but has the player-focused combat of action games - and not only did they try but they succeeded, brilliantly - only to trip up at the last hurdle: explaining this to the player. Which caused so many people to claim how much they hated the "rts sections" when in reality this was generally because those people hadn't thought to use most of the mechanics available to them. Because the game didn't make it obvious enough that they should.
By the way I am not in any way saying that games shouldn't "genre mix" or do stuff differently. Quite the opposite - once I struggled up its learning curve, I thought Brutal Legend's gameplay was fantastic, and generally I think that if we can get past the established ideas of "genre A does this, genre B looks like that" and make games as individual products, rather than "like X game but with a minor difference" then we'll see far better, more diverse games overall. But deviating from the trend and not telling anyone how to play your game is just suicide.