How far in before you quit watching?
For me it was as the kids were charging up the hill, without armor, against oncoming gunfire. Characters who had barely been identified being killed by an unseen enemy.
Loved the first movie. This one was terrible. The few positive reviews I've read here recommend watching the director's cut. Maybe it adds some back story. I doubt that it fixes the "teens throwing themselves on bullets" problem. The Hunger Games was criticized for being a poor version of Battle Royale, and BR2 manages to be a poor version of The Hunger Games.
CSB: Bought this used (but not cheap) without realizing it was a region 3 DVD, went through the work of downloading software to watch it.