Goodwin trots out familar tropes (cooking, drowning, eunuch as love god etc) to diminishing effect. The research and descriptive writing are excellent. He is very effective at creating an atmosphere; this time of Venice.
However, the main plot makes no sense (even when explained at the end) and sub-plots are either left unresolved or brought to a ridiculous, sugary-sweet and frankly intelligence-insulting conclusion. The reader will assume that things are carefully laid red herrings only to realise that they are a narrative strand that has vanished because the author couldn't work out what to do with it. And don't get me started on the 'symbolism' of the pattern that pops up everywhere.
The apparently superhuman attributes of Yashim himself are also annoying; none more so than the coup de theatre which reveals his presence about half way through the book. I know Conan Doyle used to do the same thing, but who wants a faux Holmes in a turban instead of a deerstalker? Do yourself a favour and read the real thing.