Heros could have easily been cut to 6 minutes, but I suspect the band were really giving the middle finger to the established "3 minute" song thing with all those extra parts. I bet Metallica knew they were unnecessary, but they are were thinking "we can get away with this, so let's push it" The outro I really like because it has some interesting harmonies while the melody sounds like it's descending to hell. The solo is also one of Kirk's best.
It's also a divisive album among guitar players I knew. Some really hated the tone of the guitars and called it sludge. Others like me, made me really interested in Mesa/Boogie amps.