When it comes to hip-hop I tend to only listen to albums that are considered classics, like the first two Kanye albums or The Blueprint. In general, I don't care when people say an album is classic, but I personally am assured of classic status when an album is praised as much as it is at its release as it is multiple years later.
I think one thing that hasn't been addressed yet is influence. What did the album do for the rest of the genre going forward. Obviously an album being influential and an album being a classic aren't quite the same thing -- but if an album isn't special enough to inspire other musicians to perfect their own craft I'm not sure it can be a true "classic"
The list i made before is more based on influence I'd say