Recs.
Updated
SpecsUpdate
Pros
Pro Customizable with Zephir
Zephir is a high-level language designed to create PHP extensions easily by PHP programmers with no knowledge in C.
Zephir does this by compiling directly to C and then the C program is in turn compiled to be run as a PHP extension. This, coupled with the fact that Zephir's syntax is very similar to PHP makes it a perfect way for PHP developers to use it for customizing Phalcon.
Pro Uses Volt template engine
The Volt template engine, which is embedded into Phalcon itself takes it's inspiration from the Jinja template engine and as such it's nice to look at, with a clear and understandable syntax.
Volt also compiles very fast, like Phalcon itself, so it avoids being a bottleneck for the framework's overall speed.
Cons
Con Phalcon is very buggy
Most of your programming time is spent working around issues that were sitting in bugtracker for more than five years and were never fixed.
Con Trace or debugging
Trace or debug only for the Php component or source code that you are developing. (The component developed in C language of the framework has another way of debugging).