It's not easy to get excited about the look of a PHP environment and editor but PHP Designer puts in more effort than most to create a stylish and highly usable one.
Probably the main bonus of PHP Designer is the intelligent syntax highlighting which spots errors as you type, meaning less head scratching at the end of a long coding session. This applies not just to PHP but to other languages as well. Of course, PHP Designer also comes with a debugger which can test scripts for errors and suggests possible solutions although as with all debuggers, the success rate can be hit and miss according to most users.
If you're looking for a good looking PHP editor that supports plenty of other languages too, then PHP Designer may well make your life a lot easier.