My first reaction to the song was "OH MY GAWD!! THIS IS WHAT RELAPSE WAS MISSING!! AARGGH!!!" Seriously though, the beat and attention to lyrics fits so perfect with Relapse. And content wise, it's what I had wanted from Relapse. I still bump Relapse but it's just too dark; I find it so hard to keep it on replay without feeling some sort of fucked up. "Brainless" combines dark production with a hilarious concept so well.
Also, is it just me or isn't this a blatant reference to Brain Damage"? Even the "Orange" rhymes make a crazy comeback! This adds to the idea that "Brainless" would have been great for Relapse, which was a return of Slim Shady after all.
PS: it is a Slim Shady version of "Legacy"