I think the concept of linking up Lewis Carroll's Alice in Wonderland world to the (very dangerous) imagination of Level Three (the autistic character) is superb!
As a reader, I love crisp and clean dialogue (it's one of the fundamentals of a good story for me). This was something that featured throughout Level Three's Dream (all of the dialogue reflected the personalities of each character, so that none of them were cliched or "tired one-dimensional flat cardboard characters").
I found the multicultural cast to be engaging and refreshing (in terms of individuality / expression / action / motivation), and certain serious themes were handled in an insightful way (without ever getting too long-winded, draggy, or heavy). These themes include friendship, love, death, and the family (to name a few). Simon's internal struggle with his feelings over Leah's death were some of the best portions of the text (for me), and how these feelings were presented naturally and sensitively/compassionately from the POV of a fourteen-year-old boy.
Sexuality is also handled realistically (in a way that isn't lewd or explicit) -- I think this is also something that is so important (I for one am very tired of the same old hypersexualized scenes in the mainstream mass media). This also adds an element of depth and realism to Simon and the story on the whole. I particularly enjoyed the scene where he "loses his innocence" -- while the scene was in no way graphic, it made me reflect on my own experiences [and how it must be like to feel; in my case, I don't recall any exact moment/s where I felt I had lost my childhood innocence (hmm!)...but still, it made me think about the shame/guilt involved, and how different I might feel before and after the event, were I in a similar situation as the character relating it]. Sex and sexuality are a part of human life; just because it's not thought or talked about doesn't mean it can be conveniently swept under the rug. This is precisely why I always enjoy work that doesn't commoditize and/or trivialize sex + love + relationships.
The magic in the School of the Ages series is also unique in the sense it's more cerebral than orthodoxically fantastical. The characters in this series don't rely on an array of magic wands, potions, and flying broomsticks -- not that there's anything wrong with those elements per se, but presenting magic in this form adds a new dimension to the concept of magic itself (and makes it all the more believable where we question the real world we're in, and what's real and what isn't).
There are some chapters just before the end that closely reflect the bizarre and wonderfully strange/illogical world of "Alice in Wonderland" -- I greatly enjoyed these chapters (and the poetry -- while some were slightly lengthy, they were well-written and incredibly fun! There's a play on a classic Nirvana song too *hint hint*). I felt these chapters balanced out the earlier chapters, some of which contain select passages from Lewis Caroll's "Alice in Wonderland," which contribute to the "puzzles" feel and structure of the story.
One final note about the pencil drawings included throughout the text of the various different characters. I thought this was a little unusual at first, but I think it kind of gave a personal and realistic touch to the story (visually).
A lot of hyped products today are based on "sensationalism" (because of the actual lack of meaning in the actual product?) -- Matt Posner's writing is very different and unique in that aspect. This is not to say that Mr. Posner's writing is boring or lackluster -- it means that Matt Posner handles universal themes within the context of a tale that's imaginative, yet grounded in reality. I think this is one of the strongest aspects of his writing(s), and something he should be lauded for being dedicated to with his work that's accessible to a wider audience, which includes younger readers.
Perhaps it is partly due to this trend of "sensationalism" that a lot of teen books today have a shallow appeal, so it's nice to see one that talks about serious themes in a thoughtful way that can make a difference for readers in the long term (i.e. compare this with the lusty paranormal romances packaged to tweens/teens as "fate" and "true love" -- which contributes more value to society?).