There would be no scene between Cloud and Tifa at the well. Tifa wouldn't have given Cloud the time of day, she would have gotten obsessed with boys and make up while Cloud sat around playing with swords and dreaming of being like Sephiroth.

Sephiroth wouldn't have gone insane and murdered Cloud's hometown, but would just have been an asshole who berated Cloud constantly until he finally broke down and fell into utter insanity.

Zack would have sided with Sephiroth, but kept in touch with Cloud and trolled him for fun.

And finally, Cloud would have looked Tifa up and said "Hey, remember when we were kids together?" and Tifa would have replied "Oh, yeah...whatever."

And then Cloud would have formed Avalanche because he was pissed off and had nothing better to do.

Or maybe it would be different...what do you think?