PHP has some nice OO features that I'd like to see in Perl, but also lacks some found in Perl - no multiple inheritance; traits are a very recent development and somewhat lacking compared to Moose's roles; overloading support is minimal (there's __toString, and the Iterable interface, but that's about it). I've personally always thought the introspection APIs, though quite comprehensive, are kinda clunky.

PHP's OO is a very nicely designed part of PHP; arguably the only nicely designed part of PHP. ;-) If somebody were to take the basic syntax of PHP (minus <?php), and its OO system, but strip out all those gazillion globally namespaced functions, replacing them with a well-designed standard library of classes, that would be bloody lovely.