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 verbal abuse 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.
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)?
Crowning Moment of Funny: Many consider it in the second film, when Little Jack says "Ass....hoooole" with that expressive mouth.
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."
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.
Unfortunate Implications: A lot of contrast is made between Pam's WASPy, Christian family and Greg's Jewish one. Jack's poor treatment of Greg feels very much like antisemitism, even when it's clear he does this for all of Pam's suitors. In particular when he bullies Greg into saying a Christian prayer at dinner and his bitter reaction to being given a yamaka for a gift.