The gimmicks are ideas about parallels I think - eg set in early 19th c England But Not As We Know It, a la Phillip Pullman; and story is partly (or perhaps even really) carried in the footnotes, a la Pale Fire or even [pretentious icon] Derrida. And once something's a bit clever-clever it needs to have something pretty substantial to say to carry that off. (I like David Mitchell, eg, I think he manages it.)
What does seem to me to be inherently good is the characters - far more complex and interesting (and darker) than you'd expect in the Fantasy-about-Magic this is being sold as. They are pretty substantial, I think.
I've stopped. Halfway through. Am very probably Too Lightweight for it (I like good fantasy - mainly children's fantasy, which is usually very well done/Pullman/Pratchett/Wynne Jones/Hambly. You have to, in our house, with DP around. You've never seen so many books with the title Dragon in them till you enter the portals of the Inferiority Complex).
It is under my bed, leering reproachfully at me. Should I keep going?
Or you could send it round to mine to keep The Life of Pi and dh's copy of Jonathan Bate's huge biog of John Clare company under our bed, MI!
Anyone else got fat challenging neglected tomes in need of some companionship?