This is quite a thrilling roller-coaster ride of a book. I think my actual rating is 4.5, but I decided to round up as I only had one niggling problem with the book. 
 The book opens rather dramatically with a brief exposition setting up the situation: giant asteroid, doomed world, Atlantean-descendants reappearing from outer space, only some humans may be rescued, those who are to be rescued need to qualify. 
 The pacing of this book is right on track; there are hardly any slow parts and it keeps the reader hooked wanting to find out what happens next. I think the relationships between characters are well-developed and the difficulties that would arise in this situation are also represented well. 
 Why couldn't I give it 5 stars without hesitation? Well, that requires some spoilers. (view spoiler)[After passing the semi-finals, the candidates for qualification need to pass the final, which is a break-neck race through different locks--as in canal locks--of the ancient Atlantean sub-Atlantic highway system. With a limited number of slots available, candidates from different countries are competing against everyone not in their national sub-team (each nation has 4 teams). As it works out, all the nations pretty much arrive in the final location at the same time, which is set up to be a battle royale of sorts to get to the ships hovering above and then to the planet Atlantis. HOwever, in the end it doesn't work out like this. Only one character out of millions shows any drive to push others out of the way. Everyone else just kinds of hovers around waiting for their turn in line. What? After what happened in the semi-finals, I would have expected several blues to be taking pot-shots at students of other nations. Why did everyone show up and lose interest in actually getting to the ship? In the end it felt like the author just needed to wrap-up the book and didn't have a clear idea about what was going to happen in this scene. It felt like a bit of a let-down as I think it would have worked well with the terrorist explosion happening in the midst of the chaos caused by millions of teenagers all trying to get through the narrow choke-point up to the shuttles. (hide spoiler)] 
 I highly recommend this to fans of science-fiction and YA. It's quite good. I will be checking out the next volume in this series.