Zend Server is smart in that it really only tries to maintain its core competency – which is PHP. It uses Apache 2 as the runtime for PHP, and it grabs that from Debian repositories, along with the usual chain of configurations thereof. At the time of this writing, the packaged PHP version is 5.2.8. I took a cursory look at the PHP extensions that ship with the default, and they look to be very complete.
He talks about the administration the tool offers and one thing that it simplifies - setting up some of the more difficult tools (like Zend Debugger) automatically. That said, there are a few things that bothered him: the assumption of Apache2, the lack of rollback instructions, the use of a password-only login for the admin system and the number of pre-loaded extensions that come enabled by default.