These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Should Greg have even bothered staying with Pam? In the first film, she never stood up for him against her family's nonstop bullying until the very end, and was constantly dropping little bombshells on him, such as the fact that she was engaged, that Kevin was the best man at her sister's wedding, and that her relationship with Kevin was primarily sexual.
She does a much better job of sticking up for Greg from the end of the first movie on, though.
Jack too: a Jerk With A Heartof Gold who sincerely has Pam's best interests at heart, or just a manipulative, domineering bully who likes to control other people (including his family)?
First Installment Wins / Sequelitis: The first movie was considered by many as "the funniest comedy of its years". The second one received mixed reviews, with some saying it was better than the first one, and others saying it was worse (making it a Contested Sequel). The third movie was universally panned by critics, and Robert De Niro said his only reason to work for it was money.
Funny Moments: Jack encourages Greg to test out the new safety glass on his RV by hurling a brick at it. Greg does as he's told. It bounces right off the window, and smashes the windshield on Greg's car.
The best part of the gag is Greg refusing to buy insurance for the car (its a rental) on the basis that he wouldn't need it, and Jack's response to the windshield breaking is "Ah, well, your rental insurance will cover it."
Fridge Horror: Jack has a hidden camera in his guest room. There is no justification for that sort of thing. Not to mention the fact that it's illegal.
Moral Event Horizon: Jack drugging Greg with truth serum in the second film was definitely stepping over the line. Even his own wife, who tolerated his insanity all this time, wouldn't support him after that came out.
Squick: The response to seeing Jack's artificial "breast" for assisted breastfeeding is to drown one's sorrows in Brain Bleach.
Dinah: Aw Jack, you promised you wouldn't take the boob out in front of company.
Actually, the squick really starts when you realize that Jack evidently spent quite some time somehow taking a cast of his own daughter's breast - which wasn't even necessary. The baby would have probably been fine with a generic fake breast or, you know, a bottle.