Metallica's debut album Kill 'Em All is one of the most iconic thrash albums of all-time. Part of the reason why the songs have such a dark and aggressive overtone is because all of the songs are in a minor key.
So what would happened if you played all of the songs in a major key?
Ben Eller takes a stab at transcribing the riffs from Kill 'Em All to a major key and the results are interesting. If you didn't know the riffs were by Metallica, you'd think they could be riffs by a band like Green Day, Sum 41 or blink-182.