My wife and I have watched the entire series countless times and this episode is our personal favorite. It's true. It's filmed in Italy. But that makes this episode even better as a result. Contrary to what a few reviewers have said, it has an interesting and fully developed plot that really isn't anymore difficult to grasp or any less complex or anymore contrived than any other episode.
Morse loses his perspective when it comes to the story's antagonist. He's sure that the person is guilty of something and then, without evidence and solely based on a hunch, he goes looking for the proof. In Driven to Distraction, for example, he was wrong. This time he was right. It's a typical Morse approach.
It's true that it feels like you don't quite know where things are going but such is the case in practically every Morse episode. And yes, the case doesn't come together until very late - something that happens practically every time!
Is it an implausible outcome? No. Is the story weak? No. It's quite good actually and just as hard to follow the first time you watch it as it is in practically every other episode. But in this episode you get great music and a good chemestry between Thaw and Whately, only it's set in Italy! That makes it a particularly great episode from an exceptional show.