I've probably said this a lot, but mine is The Time Paradox. I just can't get over how much I love seeing the threads from the other books kind of come together, and how well the events connect back to those of the first. (Seeing the contrast of Artemis after he has started to develop a conscience and the person he was in book one was just so epic.) And the contrast of Artemis and Holly's relationship versus what it was in the first book, and the personal crisis Artemis experiences that had been building throughout the previous books (being cold and calculating and manipulative, but having reason to deeply regret feeling the necessity to do so in a way he never felt in the previous books.) The romance was so well done, believable based on the surrounding circumstances that were set up (setting up Holly's sense of isolation from the events in the previous books, her background with her mother, her physical change back into an adolescent, etc.), but not too overbearing, which worked for me. You could really feel the sense of the personal stake for the characters in this one, and I love that.
“After all, absolutely no one can help but suspect a criminal, liar, and manipulator of committing crimes, lying, and manipulating. And of course, no one is more aware of that simple fact than Artemis Fowl.”
Opal sets into motion her most diabolical scheme yet, to frame Artemis and turn his closest friends against him. Only this time she has a new calculating partner who knows Artemis better than he knows himself. [An Artemis Fowl fanfiction, set after The Atlantic Complex.] https://www.fanfiction.net/s/8336552/1/Noble-Heart
...Shameless self-advertising, guys! C;
(And if you're really bored: http://axxonu.deviantart.com/gallery/28912232/Artemis-Fowl
AF fanart. ;J)