Writing this because existing review is so negative + I think highly misleading. I read this a few months back, really enjoyed it + I'm still thinking about it. I will probably read it again in a few years' time.
There is a kind of riddle, which is not at first obvious. It seems to be about one, fairly basic, jokey thing. But then gets deeper.
The principal character loses her grip somewhat, and all the characters, situations and meanings seem to shift. So you have to keep reworking your own attitudes as well. The end result is much deeper and more satisfying than you were expecting.