Yeah, it’s pretty amazing how the complexity of the rhymes has advanced over the years. There was a video analyzing it that came out a few months ago. I also just happened to come across this Eminem quote on Rap Genius that talked about his rhyme schemes:
“When I’m writing, I’m in the syllable game. I’m connecting 5–6–7–8 syllable phrases where every syllable rhymes. I get heavy into that. When I start rapping something, and I think of more syllables that connect with it, sometimes I want to just keep the scheme going forever.
I’ve done it before in songs, where the syllable scheme of the first verse ends up being the syllable scheme of the second verse, and the third verse — all the way down. I do it because the lines start connecting and making sense. Once I find something and lock in, it comes out pretty quick.”