Random explosions coming out of the cover art would be pretty metal..
By your standard. If your standard is that 'if an album cover is shit, it probably sucks', why did you care to check out anything up to South of Heaven? Obviously the majority of those covers suck (with the exception being (maybe) Hell Awaits). You would have looked and the cover art and said 'Welp, it's probably shit'. People deprive themselves of what is probably really good music with that standard.
On the same token, I've checked stuff out based on awesome cover art and it's turned out to be not what I expected (see: Skeletonwitch). It goes both ways.
By what standard? Slayer's first few records have fucking awesome cover art. What do you want? Michael Bay?
By your standard. If your standard is that 'if an album cover is shit, it probably sucks', why did you care to check out anything up to South of Heaven? Obviously the majority of those covers suck (with the exception being (maybe) Hell Awaits). You would have looked and the cover art and said 'Welp, it's probably shit'. People deprive themselves of what is probably really good music with that standard.
On the same token, I've checked stuff out based on awesome cover art and it's turned out to be not what I expected (see: Skeletonwitch). It goes both ways.