I think the bold defines it as well as anything. When GNR hit the scene, they were a bit different than the cookie cutter mold of hair metal that was dominating the music scene at the time, and that elevated them over the genre. Slash's guitar chops, of course, enhanced their credibility. Looking back though, I think this album essentially remains revered on reputation alone rather than its own musical merits. Sounds strange, but I think Tesla was equally talented, but their working class nature and less compelling lead singer couldn't elevate them to the same stature as GNR.
It's also still amazing that Axl's vocal range somehow ranks as the widest in pop/rock history:
https://www.concerthotels.com/worlds-greatest-vocal-ranges