Same here. Mellon Collie itself was basically my real gateway into modern music, and hearing that second half for the first time absolutely blew my mind.
I’ve said it before, but Mellon Collie has become such a staple of music collections that its sheer creativity and the sheer risk Corgan took is taken for granted. None of his peers would have (or could have) released anything like that second disc. That run of songs after X.Y.U. might be the single boldest, high-risk move ever made by an artist in the spotlight, and it was the perfect decision. Who else would / could have followed a 7 minute metal fueled nervous breakdown by a “sproingy” keyboard singalong song and a run of very atypical ballads? The contrast of styles throughout that disc is shocking, and somehow it all flows together perfectly and congeals into a musical universe.