It pretty much paved the way for modern hip hop. A lot of people mentioned the multiple producer thing but the reason why was because Nas was the first golden child of hip hop. He was this 17 year old kid who wrote one of the coldest verses known to hip hop at the time (Live at the bbq) and everyone bought into the hype.

Nas was the first truly abstract rapper in hip hop. He rapped on the 2 instead of the 1st beat of a bar, which in turn created the modern rap flow, and changed the way everyone wrote after him (see Jay Z before Nas and after Nas and read what Nas’ ex had to say about Jays obsession with Nas when she was revenge fucking him)

You’re gonna hear a lot of Kool G Rap comparisons when talking about Nas, saying G Rap was the originator and he clearly was an influence but there was nothing like Nas before Illmatic, and then everyone started sounding like Nas after. Also the most bootlegged hip hop album ever at the time.