hardest band to cover

I think people are mixing up the definition of cover. When you post things like a song would be hard to cover because of how vocals sound or preserving the original feel, that has nothing to do with covering. Covers don't have to and shouldn't sound exactly like the original song. We have the original song why make the exact same thing?

Take the Apocalyptica cover of Refuse Resist, it's the same song but played completely on Cellos, hitting the body of the Cello with the bow for percussion, and playing beneath the bridge of the Cello for the vocal portion. A song thats hard to cover should have complex composition so that it's difficult to play no matter how you decide to cover it. Not hard because of the original feel the song had.
 
Yeah, i've tried it... it is fucking hard... I play drums, and it took me three weeks to transcribe Metropolis Pt 1 note for note and play it barebones. I've got it at this point, but that is one song!