Metallica & Lou Reed - What went wrong?

It is not the first time that bands come up with the idea of inviting other artists to participate in their work.
Metallica & Lou Reed? Might work!
But at the end it didn't!

Why?
Putting some rock/blues mixed with Metal Music is a bad idea? I don't think so!
Using Lou Reed voice? Yes! Lou Reed's voice may be good for some blues...
But for this..... No, thanks.