Wow, this is turning into a great discussion!
Ya'll are mentioning a bunch of great discs....
All Eyez On Me - I don't really see this one as changing the industry, more of just a continuation/evolution of The Chronic and gangsta rap in general.
Fear Of A Black Planet and Criminal Minded - These two albums went in the direction of thought-provoking rap and sharp, intelligent lyrics. I believe Criminal Minded predated Fear Of A Black Planet, and in my view it's better, but I'd say that P.E.'s joint was more important. While BDP really put thought provoking rap on the map, it didn't really cause a lot of change (many people biting it). P.E. though, that really shook things up.
The Slim Shady LP - Yea, I think this shook things up a lot. It was the first main-stream push of lyrical content in years. (pushing it towards more brash) It was making this same push while becoming a HUGE success.
Kurtis Blow - That man's a genius. Probably as much the cause of making rap a national craze as Sugar Hill Gang.
The Score - Brilliant album, one of my all time favorites, but I don't really think it really changed hip-hop (which is a shame). After that hit, you didn't really get a big influx of music fusing reggae, rap, and killer vocals. Sure, it could be argued that it paved the way for people like Mary J Blige (vocals) or Shaggy (reggae), but the complete fusion with depth of lyrics didn't really get duplicated.
Any album by Jay Z - He's the most over rated, non-talented pop rapper today. Dude needs to stop braggen about being a great freestyler and start taking time to write decent lyrics. But then again, many I'm just getting old and cranky. :)