PHP MVC implementation without a framework
Before you consider any answer, always consider the rule that you should not write code which is not helpful and avoid code which is unused. When you are using an external framework there is a community which maintains it for you. Here its only you who is the expert. 


Less code you write, less maintenance &amp; faster development time.
More readable and maintainable code, easier it is.


Feedback on your code. 


Routes.php is quite simplistic. It is not necessarily bad but you havent considered how you would pass on different types of values.
The framework considers only routing as the primary goal of the framework. But you havent considered other things like DB query, Caching, Templating, Security. etc
You are loosing a lot of flexibility in file management when with the current routes framework.


In addition to the above I suggest including two more pieces of code.


A general file (include_top.php) which gets included in top of all files. It might look something like the following

&lt;?
session_start();
//do some global configurations
function __autoload($className) {
    // Put your own directory structure here //
    if(file_exists("../classes/$className.php"))
    include_once "../classes/$className.php";
}
?&gt;


This helps you to easily structure your code into different folders without worry about certain import statements having right path and doing additional global configurations.
An ORM (Object-relational mapping) is a must for any scalable
framework. You can checkout existing frameworks already. I will put a plug for my own light weight ORM.