Superhero sequels eventually start to suck

The 3rd Christian Bale Batman movie really sucked and so did the 3rd Iron Man film.
Yes, it had its moments but after Avengers: Assemble this was a major let-down.
The ending of the film was a twist/adaptation of the Iron Man 2 finale. Why?

The main problem with the film lie with the excessive use of special effects during the finale. 
As with Man of Steel the action was bewildering and ultimately quite boring; you we're dulled by the relentless chasing and shooting. 
I dozed off.

As with Blade 3, Iron Man felt to have taken a step back and the suit itself (or multiple suits) became the star.

The unexplained cryptic ending was hurried and confusing; perhaps intended to snag my interest for Iron Man 4? 
Well, it failled