Probably, the ability to dump arbitrary 3000-line classes into arbitrary directories. If you happened to start out working with Zend and then moved to Symfony, you might have strange ideas about how Rails is structurally too opinionated.
How much of that do you think is a good thing? Zend was essentially an unstructured collection of arbitrary classes which were more-or-less interoperable. Class names needed to be globally unique, and namespaces didn't exist, and there were no conventions about where third-party code should go, or a very effective class registry, and dependency management often meant PEAR, which was like CPAN, but terrible. The idea of having arbitrary files in arbitrary places is something that any framework should be able to accommodate, but having some sort of well-defined folder structure is really quite necessary (in my opinion). It was not really the norm in Zend, and the tools and libraries and conventions and language are all much improved since then, but it's still possible to write ad-hoc-structured code using Symfony, and there are developers who prefer this.
