Hip-hop and Rap music specially evolved with the years, with time goes by Rap music changed a lot that some of old old school rappers deny that today’s Rap music is even considered Rap music.
Since the 1979, with Rappers Delight group, rapping was interesting to listen to, it sounds like saying poetry on a beat, the focus was more on the lyrics that it is on the flow or the beat itself. This sound of Rao stayed the same until the late 80s with Rakim and other rappers that sounds a bit different, the flow of the rapping was more musical and the beat seems to have more than just a kick and a snare and a couple of Hi-hats.
Rap Music took a different round in early 90s, with 2pac and Biggie, Ice cube, Dr.Dre, Jay Z and Snoop Dogg, the music of Hip-hop was rich of melodies and included R&B singers, this is the Era more recognizable because of the influence it had on the whole world not only United states, and also the technology of making music was also improving and helped create some of the best sound of Hip-hop.
Late 90s and early 20s had Eminem included, Eminem and other artist who brought new sound and new perspective of making Hip-hop music pushed the culture to another level, it is like if they proved that there is no limit, as long as Hip-hop music is attached to its basic lyrics’ complexity and poetry, you can do with whatever you want.
Late 20s and todays Hip-hop music is very different, Trap came along and the fans are now more attached to how things sound and hype of the music more than it is to the message or the art of putting the words together, Hip-hop nowadays is going thru a time that after a while, one of 2 will stay, sound or lyrics.