Anyway, the movie is faithful to the book for the most part-- as faithful as possible, except for the unnecessary sex scene (nothing too graphic, but as my son said, "I still know what they're doing!") and a few minor plot points. Movies based on books the size of The Host always suffer some loss of material.
The most glaring problem with making this story into a movie is the fact that much of the dialogue in the book happens inside Melanie's head. This made for an awkward voice-over narration type of thing whenever Melanie wanted to talk to the alien that took her body, named Wanderer. I can't imagine any other way they could have staged it, but it was stilted, especially at first, and I felt I could picture the actress in a studio saying the lines into a mic. Didn't come out believable.
There were some weak acting issues and some rather obvious plot holes (the biggest of these is the question of how the first "soul" got to Earth and invaded the first human, since they are basically large, pretty, silver, glowy caterpillars with many tendrils, but arrive helpless in a little pod and have to be placed into their hosts by "healers"-- humans who have already been taken over. How could they have even begun such an invasion???) and some very long sequences.
The scenery is pretty, but onscreen, once you've seen it three times, you hardly need the vista sweeping across the screen 98 more times. Okay, already!
It's also amusing that supposedly the aliens have removed all human nature, including greed, violence and such evils, but there are some who drive shiny silver Lotuses and fly around in equally shiny silver helicopters and they dress very, very well, while others look more like average Americans.
Even the cave-dwelling human survivors seem to be inexplicably well dressed, too, at least during the second half of the film. I thought that was kind of funny.
Also funny was how my poor son (I made him go with me when my sister got sick and cancelled-- non-refundable tickets! They had to be used!!) reacted every time Melanie kissed someone. And she did a LOT of kissing. Like every other scene... I had no idea it was a kissing movie... even though I've read the book...
Would I recommend it? To fans of the book, yes. They've probably already been to see it, though. If you're not a fan of the book, you probably won't like it. It isn't a very exciting sci-fi action movie, and the story suffers quite a lot from being smashed into movie-length.