- D3 is built around all the normal web stuff like HTML, DOM, CSS, therefore there is no need to learn new technologies in order to use it.
- D3 is rather like a programming language for graphics. Leave aside the fact it’s written in JS, and it looks more like a Processing type of interpreted programming language.
- D3 has a big community behind it. While even 2–3 years there were still problems finding good documentation for it, right now however there shouldn’t be any issues with it.
- As other answers have mentioned, you can think of D3 as more of a basic utility that can be used to develop higher level charts/libraries, and as it turns out there are many of them. They are not better than D3, but rather they use D3.