I got Brutal Legend right when it came out years back, and I was pretty disappointed with it for the price I paid. I might have been ok with it for $5. It was not at all how I thought it would be from playing the demo.
The RTS stuff it introduces later is not very good. I beat literally every single RTS section using the same strategy, and a lot of the units they give you aren't even worth bothering with. The game would have been much better as a standard action RPG like Fable. I actually thought that's what it was going to be until it sprang the RTS junk on me.
There's also not much variety to the side missions. There's a couple of unique side missions, but everything else repeats over and over. Also, from what I can recall, the story is super predictable.
It definitely was never worth its launch MSRP, buuuuuut for $5... maybe?