Nothing really happened in this book. The plot basically consisted of America being with either Maxon or Aspen and realizing how much she loved whoever she was with and how much they loved her. They'd then go away, and she'd start questioning whether they actually loved her or not, despite her dramatic realization. Then she'd be with the other and have the same realization. This cycle repeated throughout the book.
The caste system continues to make no sense. Neither does the Selection. There is a challenge where the girls must plan events for foreign diplomatic visits. They have only a few days and no help or real training. No wonder their country has multiple wars going on if they do stuff like that when diplomats come to visit.
And the girls had to then create philanthropy projects to present to the country. I don't think they know what philanthropy means because the suggestions tended more toward reforms in policies.(show spoiler)
The rebel situation also continues to be a joke. I can't believe the guards are so incompetent that rebels can get into the castle so often and do so much damage.
And the fact that Aspen keeps pursuing a relationship with America and she one with him gets ridiculous when you consider that they literally can be killed for doing so. Or the sentence can be reduced, and they get whipped and then thrown out on the streets as Eights. Although Aspen's also the same guy who sneaked into her room at night while she was sleeping in the castle, which I always found creepy, so the lack of care for America's safety doesn't actually surprise me.
The one thing I felt the first book had going for it was America and Maxon's romance, which was cute at times. Not so cute in this book. It got ruined with America's endless questioning and lack of trust and Maxon's possessive and jerkish tendencies.