I endorse Bazooka_Joe's review.
The author, Stephenie "Twilight" Meyer, says that The Host is science fiction for people who don't like science fiction. How true that is. Ms. Ronan gives a good performance under the circumstances, so there's that.
For a longer, scene by scene review, please see here: http://www.yourmoviesucks.org/2014/06/yms-host-part-1.html .