This was a pretty funny book but don't expect a 'deep' read. Characters are not particularly well-developed, although many are very funny. The storyline of the quest for the stones isn't bad overall, but the whole thing is really the kind of light and funny read that you might take on holiday with you/read on the plane etc.
Its plot, characters and relationships are definitely not deep and meaningful but I quite enjoyed it all the same for its sense of humour.
I think I would read future books in the series or others by Evanovich, but only in between other books when I needed a bit of a break from anything heavy.