I'm a much bigger fan of Pearl Jam than I am of Nirvana, but I give Nirvana more credit for "changing" the music scene (not that they were trying.)

You are spot on that musically, Nirvana's song structures, lyrical content, etc. are nothing to write home about. And that's kinda the point. They took a minimalist approach to rock at a time when overproduced, formulaic hair metal was dominating the charts.

In my mind, the secret to their success was two things. The first is timing, because Nevermind came along at a time when rock really needed a new direction. More importantly, I think that the Nevermind albun was heavy enough to bring in the recovering metalheads, visceral enough to pick up some leftover punk rockers, yet still polished enough to have pop appeal.

I also give Butch Vig all the credit in the world for harnessing the raw power and anger of Kurt Cobain and turning it into a monster record that millions of people wanted to listen to over and over. I remember the first time I heard Smells Like Teen Spirit came on the radio as if it happened yesterday, and even though it wasn't my cup of tea at the time (I was heavy into classic rock back then) I could tell it was going to be big. I never thought it would spawn a totally new direction in rock, but that single really jumped out at you and forced you to listen, even if you didn't like it. This made Nirvana seem more revolutionary than Pearl Jam, Soundgarden, etc. even though that may not be the case when you listen to the other Seattle bands who *didn't* get picked up by the big labels.

Also, STP don't really belong in this discussion. They were really part of the second wave of grunge (Core was released late in 1992 and didn't get airplay until 1993) and IMHO a blatant ripoff of Pearl Jam. They did have some good tunes along the way, but they were definitely derivative of the first wave of grunge acts.