Mostly superior quality and consistency. With the beats rhymes and concepts. Has to be some impact - otherwise I'll call the record a personal classic.
Classics from 1998
IDAHIH
Capital Punishment
Moment Of Truth
Mos and Kweli
That's just off the top. I could be forgetting others.
all these albums have somewhat of a similar sound.
"flesh of my flesh" doesn't fit the mold.

so these forgotten songs that people never bump,had little impact when they dropped are classics and you have to ask such a question about flesh of my flesh
ok,they might be classics in your bedroom,on your stoop,hallway etc but thats it