It supports tons of languages, including HTML, PHP, JavaScript, etc…
Some of the things that stand out to me: Macros, Multi-document sync’d scrolling, Vector-style zoom in/out, and Code highlighting that is on-par with Dreamweaver. It also has comparable site-wide find and replace. Another nice feature are tabs that behave like Firefox. They are draggable, and a middle-click closes them. Anything I could say won’t do it justice. In short, what Firefox is to the browsing, Notepad++ is to code.