PhpStorm is the product of a company that also makes Java IDEs, in this case JetBrains, which may be better known for the highly regarded IntelliJ. JetBrains' PHP tool, however, doesn't come integrated with its Java tool, unlike many of the other IDEs described here.
I suppose there might be some developers who are creating hybrid PHP/Java applications and might be disappointed by this, but I don't think there will be many. It's still possible to run both IntelliJ and PhpStorm on the same machine.
PhpStorm exhibits much of the same attention to detail that made IntelliJ popular. I still find IDEs like Eclipse to be a bit arcane, with their complex trees that often hide important jobs in some deep corner of the hierarchy. The folks at JetBrains have done a better job of cleaning up the UI and putting the buttons in places that are simpler to find and understand.
All of the colouring and completion are here, but in a simpler form. Not that PhpStorm is simplistic, for instance, there are six different pre-integrated source control options, more than you'll find in the other tools.
Configuration benefits from a number of wizards to assist you in getting everything connected. While the other IDEs offer some fields that either work or don't, PhpStorm takes things a bit further.