A whole lot of alien invasion. A little bit of teen angst and romance. Chloe Grace Moretz kicking butt. Yep, it's another movie based on a series of post-apocalyptic YA novels, but unlike the big-name franchises, I'd never heard of this one. There's nothing in THE 5TH WAVE you haven't seen or read before, but it's fairly well made and reasonably entertaining. If they make movies out of the two sequel novels, I'll probably watch 'em.
There is one wince-inducing gun mistake, but I was never sure if it was ignorance on the part of the screenwriters (or the author of the source novel), or if it was a deliberate mistake used as a bit of characterization. I lean toward the former.