Every feature is optimized what Notepad does not have. You cant ever imagine of that until you download and try it. Under the GNU license, have stability also to run on your machine.
For coding as PHP language, Notepad++ is a great choice ever. For HTML source code, the best editor is here.
For me, what Notepad++ is great for use is:
1- Syntax highlighting(color and detect)
2- Low memory use
3- Tab system(same as firefox)
4- Various plugin
5- Able to replace text(easy and more than Notepad)
6- Link detect
And more much more...
Here Notepad++ on my machine:
|Notepad++ on the run|
You can download Notepad++ in their website here(http://notepad-plus-plus.org/)