Ranked in these QuestionsQuestion Ranking
Pro Concise tutorials
The tutorials are written in a way that makes them clear and informative without being bulky. Due to the tutorials being example-heavy, you are able to see the concepts learned in code after every step.
Pro Easy to work through only what's relevant
If you have a specific project in mind, the set-up of these tutorials make it easy to read through the chapters only relevant to what you need, without feeling lost.
Con Doesn't go into detail
These tutorials are a great place for a beginner to start, but if you want to do more advanced things with the library then you'll have to continue with another resource. However Scott Murray has a book, "Interactive Data Visualization for the Web" that extends his online tutorials.