Sequels thought to be better than the original:
I don't actually agree with some of them, but the following appear to be known for being better than the original.
Superman II (1980)
Aliens (1986)
Terminator 2: Judgement Day (1991)
The Godfather: Part II (1974)
Lord of the Rings: Return of the King (2003)
The Dark Knight (2008)
Mission Impossible: Ghost Protocol (2011)
National Lampoon's: Christmas Vacation (1989)
Star Trek II: Wrath of Khan (1982)
Toy Story 2 (1999)
10 Cloverfield Lane (2016)
Lethal Weapon 2 (1989)
Any others???