Is there an overall message/moral in this?

I actually thought that the moral creeping in at the end was at odds with some of the earlier scenes.

The second half of the second part seemed to be wagging its finger at Casanova. The culmination of his depravity was, of course, the scene with Jack in Naples. Likewise, the scene with Old Casanova where he rails at Edith and chases her away was getting pretty dark.

I enjoyed those elements coming in to play to show the dark side of Casanova. His perverse side was played mostly for laughs and his capricious nature was romanticised during the flashbacks. I thought that they were going to spin our heads around, make us dislike this fellow whom we have fallen for thanks to Tennant's charms. But, ultimately, I thought they didn't go far enough. It seemed only lip service at the end and the weight of those dark scenes never balanced or surpassed the uproarious fun of the flashback/story scenes.

It was a bit like much of Baz Luhrmann's work, really. Consider Gatsby: we're supposed to find ourselves disdainful of the vapid partying, but Luhrmann is so keen to make his party scenes look marvelous that we never really dislike the notion of being part of that crowd.

For the record, I do like Gatsby, just as I like Casanova, but I felt like Casanova didn't twist the dagger in the right places, so to speak.