These movies are done. They are past done. Yes, The Hangover was a genuinely funny movie, but the warm feelings towards a well done piece of entertainment are not enough to make Part III anything more than rote.
Human pain and humiliation may be the essence of comedy, but animal cruelty is hardly funny. The third Wolfpack film touts its giraffe decapitation in its trailer; it also includes the smothering of a chicken with a pillow and the poisoning of dogs.