My opinions about The Infinite Sea are about the same as for The 5th Wave. I enjoyed it, it was suspenseful, but there were still a lot of imperfections. 
 My biggest problem with these books is the romance. Well, I've never been through an apocalypse, but I imagine there's no time to think about which one of the two hot boys you should kiss. 
 Yancey scared me so much when Grace said that (view spoiler)[Sam was dead (hide spoiler)]. He scared me on a lot of occasions, so bonus points for that. 
 The characters are quite good. I'm not a big fan of Cassie, though. I honestly prefer Ringer. The scenes that included Ringer were very well-written, especially when (view spoiler)[she was thinking whether to kill Teacup or not (hide spoiler)] or when (view spoiler)[she escaped the hospital where Vosch was keeping her only to discover that everything had been a test (hide spoiler)]. 
 Overall, it was a pretty good book, but it doesn't deserve more that 2.5 stars.