Four things have made me appreciate Dygraphs:
- It's got an wide array of configurable options.
- It has an active community on the mailing list.
- The documentation continues to improve. The options listing above was a recent improvement that is now my regular go-to reference.
- The tests. Really I should call them examples. Because I can just often analyze them and get 80% of the way to the solution of the problem I'm working on.
If you need a graphing library I recommend you give Dygraphs a try.