Ranked in these QuestionsQuestion Ranking
Pro Extremely fast
Since the framework is and extension built in C it's extremely fast and efficient. It's actually one of the fastest PHP frameworks, and according to some benchmarks it's the fastest framework out there.
Pro Open source
Phalcon is open source and is available under the BSD License.
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.
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 Loosely coupled components
Some components can be used as standalone packages like models, views, etc..
Pro Very flexible project structure
You can set up the base project as you want. It's very flexible
Pro Clean and light project code
Since the framework code is not in the project directory, the code is light and clean.
Con Require good programming skills
Not so easy to use if you want to gain the best from it.
Con Debugging requires knowledge of C
You need to be a C programmer to debug Zephir or C code. Or if Phalcon is not maintained anymore and you have a problem and don't have much skills in C, you will be hard-pressed to find a C programmer to fix it.
Con Not for shared hosting
Phalcon needs root access to install the PHP extension which is written in C. Developers who plan on using Phalcon must use VPS or Cloud Hosting with root access available.