I think the thing I liked most about this book is Artemis' ongoing descent into craziness. I quite like the character changes of Artemis between the last book and this one; the obsession over numbers was amusing to me and seemed a logical addition to his character (whether because of an illness or not). I also like the indepth attention towards the placement of objects and other OCD-like qualities. Many of which I'm surprised he hadn't developed earlier, especially considering his attention to detail and elaborate planning. Although, as amusing as Orion was, I think his entire being was a little over the top. As I understand it, Orion is a mixture of various subconscious elements including books, movies and Artemis' excapades, as well as odd things such as the love he doesn't express. Yet his complete romantic attachment to Holly and subsequent humourous elements ("I'm the nut!") to his condition seemed a little bit unnecessary, especially considering his character. However, he seems to be compiled as a complete opposite to Artemis. His composure seems like he has little care of shame or embarrassment, complete unlike Artemis; Orion seems prone to outbursts and proclaimations of love.
However, on the other hand, I do like how this craziness of Artemis allows Mr. Colfer to pay more attention to the other characters and gives them the chance to blossom their own intelligence. In the prior novels, though all the predominant characters- Holly, Foaly, Butler, Juliet and Mulch- are able to take care of themselves, but Artemis' plans ultimately run the show. In The Atlantis Complex, the condition allows Artemis to take a back seat so that Holly and Foaly discover the majority of the plot for themselves and it allows them to solely take care of matters. That is not to say that Artemis is entirely useless; eventually he gains moments of (relative) sanity and still manages to come up with various plans (some even including his mysterious counterpart).
The character development with other characters seemed good as well. Firstly, I liked Juliet's wrestling career, though was a bit disappointed with the fake wrestling, considering it seems completely against her ideals in the first book. As for Foaly's characterisation, I like the way we get more insight ot his family; that he has children now and the way we get to read more of (even though it's a little bit) his other family like his nephew. I like the way Holly is developing other love interests as well (despite Orion's advances and the kiss in the last one) like the several dates with Trouble. Butler seems like his character is advancing as well and he is definitely become more of a friend to Artemis. I like how he has clearly recognised the symptoms of Artemis' illness.
I liked the introduction of the other Root brother and quite enjoyed the events surrounding his escape. His past intriqued me as well and enjoyed how he had fallen in love with a human and his endeavours ended up to try and free her from her old age. His escape plan was amusing and I enjoyed his interest of runes, especially with the way he used them against Vishby, Holly and even Artemis.
-I think the opening sequence went a little too long; the droning of Artemis' speech seemed a little awkward to read. It was completely to alert us to his condition, but felt it didn't need to go on for so long. On that note, I think it was out of character for Foaly's heckling during the show and tell. Also, it seemed a little like Holly was trying too hard to seem jovial. I was a little disappointed by the death of Vinyaya as well; I liked her character and it seemed to easy for her to be killed off, much like the death of Root a few books prior.
-The miniature history of Atlantis was interesting, though I wish we'd gotten to read a little more about it, especially the (non-prisoner) inhabitants.
-I thought Artemis' mother was a little useless in the novel, but I do understand her little bit of input; it anchors him and reminds the reader that he is still only a child (essentially), especially considering his time travel.
Overall, I enjoyed the book and think it was much better than The Time Paradox. The book had a great premise, including Artemis' condition and the escape of Turnball. Though, to be honest, I was half expecting Turnball to be a victim of the Atlantis Complex as well. Mind you, it all ended well and I'm torn with trying to figure out what rating to give it. I'd like to give it a five-star rating, though I admit it isn't perfect. I think 4.5 stars is fine.