I'm not really a fan of either (I liked some old Metallica stuff but they really lost me with the Napster deal, Lars showed his true colors with that) but it sounds abstract enough that I think it could either be a huge disaster or it could turn out to be a brilliant piece of art that gives a boost to both careers. Just look at Robert Plant/Alison Krauss and Elton John/Leon Russell, both of those albums looked like potential failures and they turned out to be Plant's biggest album in 20 years and Elton's biggest in 15, and both albums were critical darlings.