By skyforbes I can think of several examples where many people seem to think the second installment in a series of films is the best one. Ironically, most notably superhero movies.
Spiderman 2
X-Men 2: United
Blade 2
Captain America: Winter Soldier (2nd installment)
The Dark Knight
Empire Strikes Back
Wrath of Khan
I am sure there are more out there that come to mind.
There are also film series out there where it could be argued that other later sequels are better than the first installment, or maybe even the previous installment.