Hm, difficult to say. I wasn't as hooked as I expected (The-Hunger-Games-hooked, say), and I didn't empathise with the characters enough...(reason I would give it 3 stars). But I also can't find any real fault to it. It's well written, well thought, and the plot is rather airtight (reason it kinda deserves 4). 
 I think it was too introductory--the ending works veeery well, so it's probably a good thing it ended there (considering it's a series, of course), but then I would have made the rest of it more compact, and cut out some parts from the beginning. 
 More eloquent review coming this weekend!