I've seldom seen books about which my friends' opinions differ as much as with I Am Number Four. They either seem to hate or love it. For me it is more complicated though.
The story is not very original but features two types of aliens battling their war on Earth. Of one of the parties, only a handful survive: nine Gardes and their companions who have to train the Gardes while they -obviously- develop a set of super powers. Another complication, these nine Gardes all have a number and can only be killed in that order. One, Two and Three have been killed. The main character is Number Four.
It was a very fast read, but at times it was far too much of a soppy teen drama instead of the sci-fi book I wanted to read. A large part of it is filled with the romance between two not too interesting characters. I could certainly do without that. But somehow, it didn't feel as a bad read because it was so fast so I continued the series.