I mean really, Empire Strikes Back went outside the box of sequalls and defined a lot of modern day seconds. Bird, even your Toy Story 2 ripped off Lucus with the bad guy being the good guy's dad. Oops, spoiler alert.
I think every decade there is a sequall that sticks out as the best of that generation. Terminator 2 in the 90's, The Dark Knight in the 00's, The Avengers in the 10's, and for my generation The Empire Strikes Back in the 80's.
For the record if your a baby boomer, the sequal for you in the 80's was The Color of Money. (Where Paul Newman does something no other actor has ever done, wins an osacar for the same roll twice!
And no, Rocky II was not the sequal of the 70's. The Godfather part II set presidence there my friends.