I absolutely loved it. It had a very black and white mystery movie feel to it and a general creepiness. To be fair I spook easily, but I was up till well past my bed time trying to finish.
I read special topics way back in its hey day and later the basic eight which made me raise an eyebrow and rethink just how talented of a writer Pessl is, but this one really knocked it out of the park for me. I thought the characters were a real step up from smarty pants Blue. Although Scott being a down on his luck investigator with an ex he still pines for is a bit of a cliche it works.
Over all I was very entertained and at times more than a bit frightened. Well worth the price of a hardback and I would highly recommend it.