In general, I found that my favourite books of the Metamorphoses were those that contained large number of changes and were clearly focused around a theme. This is the case for my favourite book of them all, Book 3. At Latin camp last summer this was one of the texts that we translated, and so it was a nice reminder to reread the stories again. My favourite story is also in this book, that of Actaeon and his hounds. This story has many excellent features, most notably the description of the metamorphosis and the irony of Actaeon being torn to pieces by his own hounds ('Spot' being a personal favourite of mine).
Conversely, my least favourite parts of the Metamorphoses were the epic catalogues, such as the Battle of the Lapiths and Centaurs (Book 12), as they tended to disrupt the flow and make for rather slow reading (although the gory details tended to make up for this).The exception to this was the story of the Caledonian Boar (Book 8), as the mockery of the famous Greek heroes made for rather amusing reading.
Overall, I really enjoyed reading the Metamorphoses as a fine example of Ovid's wit and poetic skill, and if I had to give it a score I would put it at around 8 out of 10 as a staple of Classical literature and well worth reading. It has its good sections and its bad sections, but is remarkable in its ability to enthral and entertain 2000 years after it was first written. Thank you for reading, and if you've read the Metamorphoses yourself then leave a comment and let me know what you thought of it.