The best selling debut album of all time has sold well in excess of 33 million copies. Not bad for a bunch of skinny kids from the LA club circuit. It doesn't matter that the third best heavy metal album of all time is a hard rock record. For many people, this is the best album of all time, regardless of genre.
Tom Morello: “From top to bottom, it’s the embodiment of lightning being caught in a bottle. An unbelievable combination of band chemistry, great rock and attitude, brewed to perfection.”
“Maybe it's more of a hard rock record, but for me, as a complete, all-killer LP, it's probably Appetite For Destruction.” (Thanks, ChrisVinnicombe)