I started watching this without any prior knowledge. Ultimately, it is not that special, but also not that terribly bad. It's obvious the makers played it safe. It's ultimately a mix of a high-school teen movie and a soft-core SF. The high school section contains all the cliche ingredients: the jock (quarterback, of course), a cheerleader, a nerd who's constantly harassed by the hunks of the school, the newcomer John who's not bad looking but is seen as if he's an alien (what a coincidence). Off course John will defend the nerd and is immediately attracted to the cheerleader at first glance (melt, sigh, swoon ...). How obvious. You can feel a romantic love relationship coming up. So the main and largest target group, the giggling teenage girls, is satisfied now.
And now we have to add something so the boyfriends are satisfied enough to accompany those teen girls to the cinema. John is one of the survivors (No.4 of course out of 9) from the planet Lorien who were exterminated by the Mogadorians. These Mogadorians are almost a copy of the Sith's from "Star Wars". They are chasing these Lorianen (Loriethers, Loriers ...??) to exterminate them. The reason why is unexplained. Of course there was in the infinite universe only one planet where they could hide : Earth. And on earth starts a battle between those two alien races.
Apparently this movie is an interpretation of a book. For me a decent adaptation is one you still can understand despite you haven't read the book and eventually you know what it is about. However, this adaptation leaves many unanswered questions: what is that damn box, why should they be eliminated in that order, what is the meaning of the necklaces...
There are also positive things to enumerate. John Smith plays a decent rendition. Sarah is a beautiful appearance and Nr. 6 looks so delicious I could eat her. The Mogadorians are tremendously funny sometimes and the film also contains other funny dialogues:
Sheriff James: Who the hell are they?
Mark James: Big-ass linebackers?
The ending of the movie was fairly successful done in terms of effects and action. Even the swollen dog that had to fight against the bat-like hell hound in the showers, was quite enjoyable.
Conclusion: A simple teenager feelgood movie with a portion SF action.