The Maze Runner by James Dashner succeeds in many ways. The main character is likable and sympathetic (if gifted with enough advantages that he is more "hero" than "everyday guy"). The construct is intriguing -- I especially liked the giant maze walls rearranging themselves at night. And the monsters are certainly monstrous. Dashner is a genius to combine robotlike features with a slug!
But the book does what far too many "first in a trilogy" books do. The conclusion is all about setting up Book Two, not paying off Book One. I understand cliff-hangers and all that, but I do think it's possible to make an ending satisfying and still leave readers anxious for the next installment.
When I've hung in there with a story for 350+ pages, I think I deserve a few pages devoted to a real ending. I want the characters to have a moment of triumph or insight that lasts longer than dinner.
Is that so much to ask?