Our own Morgan Meis in The Smart Set:
The fact that the Beastie Boys were rappers made it all the more difficult. Rappers don't sing; they rap. So harmony is out. There will be no blending of voices. No barbershop tricks were going to solve the problem for the Beasties. These three fellows from Manhattan and Brooklyn would have to develop a new style of rapping altogether. The style was perfected on their second album, Paul's Boutique, but it was already present in their debut album License to Ill. Maybe the fact that the Beastie Boys started almost as a gag (three white Jewish kids from New York make a rap album) had a freeing effect on their music. Taking themselves less than seriously, they were able to have a loose approach to rhythm and lyrics. They would finish one another's sentences, combining thoughts and rhymes, as if their three-partite mind was connected bodily and spiritually.
Without exactly intending to, the Beastie Boys helped solve one of rap's biggest problems in the early- to mid-1980s, which was rap's simplistic rhyme scheme. Early rap can often feel like a nursery rhyme set to music. The rhyming is too often obvious and formulaic. The stress is always on the last syllable of the line. No offense to Kurtis Blow (an innovator in his own place and time), but the lyrics to his less-than-fantastic song “Basketball” are a case in point:
Basketball is my favorite sport
I like the way they dribble up and down the court
It is straight iambics all the way through, with a hard caesura and stress to end each line. In a word: boring. (Blow's thoughts on basketball did not exactly kindle the imagination either, but that is another point.) Something had to change.
More here.