Like I said though, I was born in '93 so I might have had to really live in the 90's as a teenager to see what was so special about Nirvana.
Nirvana blew up the Seattle grunge scene and made it mainstream. After Smells Like Teen Spirit came out, there was a period of half a decade where if you turned on the radio, you were gonna hear grunge. Ton of bands (IE Pearljam, Alice and Chains, Soundgarden) became popular because of what Nirvana did. Cameron Crowe ended up making Singles because grunge was everywhere, and the Singles soundtrack ended up becoming one of the best soundtracks of all time.
What Nirvana did for Seattle grunge was kinda like what Dr. Dre did for Los Angeles G-Funk - took a style of music nobody knew about and blew it up overnight.