Nice work! A micro-micro-framework, makes Slim and Silex look big.
For example, why is ReflectionClass not used (I'm guessing PHP 4 compatibility)? Particularly because class_exists can cause major headaches if you use the default autoloader, see https://bugs.php.net/bug.php?id=52339
There's also little information available from outside the router; an invalid class/method uses die without giving you an option to check for it and handle it some other way. I also don't immediately see any special handling for not allowing magical methods to be called
Definitely a good start for personal projects though, just needs some spit and polish