I don't think I've met anyone who didn't love the first half of this film, but I have heard of people not liking the second half. While I like the first half more, I like it more by just a touch. The whole film is flat out amazing.
The thing about the first half that is amazing to me is how fast it moves. While watching this time, I looked down at the run time when it was finishing and noticed that 45min had gone by when it felt like 15. This section starts off humorous for sure. All the phrases used to put down the new soldiers make me laugh, and different reactions to them as well. Then, the longer we go into the sequence the more we start to feel how dark this is. The tone shift is wonderful, and sets you up for the halfway finale.
The second half does the same thing, but in a totally different context. Joker starts off using humor to deflect what he's feeling, but then by the end you really get into his emotion and personal conflict. That last major shot (no pun intended) makes you stay with him and his reactions instead of seeing everyone else.
Frankly, this is one of Kubrick's best films, and that is saying a lot.