Way back in the day, 'bout fifteen years ago, the planet Lorien was attacked, and destroyed. Fortunately, a few of them escaped to Earth. Nine children total, each with one Cepan/guardian. But the Mogadorians, the race that destroyed Lorien, found out about the escape attempt, and have been hunting the nine ever since. One, Two, and Three have all fallen, and now it's Four's turn.
Four is a teenage boy who's had many, many different names. When he moves to Paradies, Ohio, he takes the name of John Smith (reeeeal inconspicuous). John knows he's next, but luckily, he's developing his legacies/powers. Unfortunately, they aren't very predictable and they take a lot of time and work to hone. Also unfortunately, John and his Cepan, Henri, don't have a lot of time. The Mogadorians are after them.
It may not sound very complicated, but it actually is. I was surprised and pleased to find that Lore really worked on the details to make everything work, and he took the time to explain things without it all getting too tedious. The Loric race(s) are mostly developed, and Lore provides good background on the way they used to live back when they had a planet.
Now for the plot. It's a straightforward thing (teenage boy runs from aliens), so not many people would have a ton of trouble executing it. Lore certainly didn't. He made the characters likeable, and while they didn't have extraordinary depth, they weren't just flat either. Sarah, John's human girlfriend, isn't infuriatingly annoying like most love interests, and John's best friend is pretty awesome (most of the time). One bad thing about the characters is that almost as soon as you start reading, you can tell who's going to die. I picked out all the "dying" characters and all the "surviving" characters, and - bingo! - I was right.
Here's what I liked most about I Am Number Four: It wasn't about John and Sarah. It was about John being a Lorien and trying to survive on Earth, dodging Mogadorians and the chance human who happened to get suspicious. And here's what I hated most about I Am Number Four: The ending climax. Every chapted near the end ended with John about to die, and he was always preparing himself, thinking "Well, this is the end, we had a good run", and every time it works out fine. It isn't even suspenseful, because you can tell he's not actually going to die. It was getting very old be the end, and everyone knows that if you have a good finish, it practically makes up for any other mistakes you made. And if you have a bad finish...well.
And then there's one more thing that taints the memory of I Am Number Four. The movie. Now, I haven't seen it yet, so I could be totally wrong, but I have seen the trailer. It looks like the movie is moer about John's and Sarah's romance than the aliens. Talk about a letdown. I'm still going to see it - eventually -, but I have very low expectations at the moment.
In conclusion, I Am Number Four is a surprisingly good science fiction novel, with more details than you might expect (plus more magicky science), and the bonus of it not being about a forbidden romance. It's definitely worth a read, even though it might not end up being your favorite book.