My rating scale:
100% The greatest thing ever, and you're only reading the review for entertainment, not cos you don't have it. Right?
90-99% A transcendant masterwork that elevates beyond a great metal album, and is simply great music. There shouldn't be more than 50-60 albums with this ranking in my review section.
80-89% A Metal classic. It has a flaw or two, and doesn't really rise above the metal tag, but it's still essential.
70-79% an album that I thoroughly enjoy, but I can't wholeheartedly give it 4 star status.
60-69% A slightly above average album, probably has 5-7 good songs on it, but nothing more.
50-59% Guilty pleasures or simply average albums. Nothing I would bring up in a serious conversation of the greats.
40-49% Really bland or mediocre. Has maybe 2-3 good songs I give repeat listens, but as an album, it fails.
30-39% This kinda sucks. If it's from a great band (Satan forbid) I'll listen to it once every two years to try and convince myself "come on! it's (band x)! It has to be great!" Then I listen to it and go "nope."
20-29% This really sucks.
10-19% AAARRRGGGHHH!!
0-9% I'm sorry, but if you genuinely, unironically think this is good, you should be henceforth banned from any discussion about metal. Better yet, banned from discussion from music. If you like this, I can only imagine how horrible your taste in pop/rap/country/punk must be.