This may very well be the first series I've read where I've rated every book in the series with 5 stars. Far too many trilogies I've read seem to weaken rather than gather momentum by the 3rd book. I think that it's either because the author unsuccessfully tries to use the same formula that worked well in in the first book across all 3 books or they try to stretch out a 1-book storyline over 3 books. I think that the Across the Universe trilogy works well because each book tells a very distinct story and each book reveals its own "secret" at the end without revealing the big "secret" that ties them all together until the 3rd book. In fact, I'd say that the 3rd book could stand alone quite well by itself and that I'll count it among my favorites.
The first 2 books of the series tell of a ship that has been traveling for hundreds of years to reach an alternate Earth, a girl who wakes up too early from her cryogenic sleep, and her growing relationship with the ship's young ship-born leader. The 3rd book is the payoff book where they finally reach the planet they set out to reach centuries earlier. Upon arrival on the planet, their first contact with Earth in centuries is lost and it becomes apparent that the planet is filled with deadly beasts and plants. The story becomes even more of a horror tale as someone or something starts to kill off the new settlers. Is it the pterodactyl-like creature they've seen in the skies or is it someone or something even more sinister?
I've heard that Heinlein and probably other authors have touched upon the themes of this series that are far too spoilery to mention,. But even if these aren't completely original ideas, the author has presented them in a very interesting way within the YA genre. I could have done without the awkward YA kissing scenes in this last book of the series. But, other than that, the book was quite strong. It was filled with the perfect balance of mystery, secrets, and horror to keep me theorizing to the end. Once the final secret was reveiled, it made so many things in all 3 books finally make sense. And the new planet that the author created in book 3 was well worth the 3-year wait to discover it. The series ties up nicely at the end and begs for a movie.