Here's the main issue with The Hangover III
The first two installments (in addition to significantly funnier scripts) followed a particular formula that made them interesting: THE HANGOVER.
The first two movies both had the protagonists waking after the night of craziness, and spending the rest of the movie pricing together what debauchery occurred in order to solve problems that were created.
They were fun puzzles to watch get pieced back together.
The Hangover III involves NONE OF THIS. It was a significant disappointment when compared to the first two. It just wasn't fun, nor was it very funny. Too bad.