As a teacher I understand how difficult it is to explain complex topics in a simple step by step way.
The site has some really impressive technical aspects, but the educational angle is the most rare and special! The simplicity of the language and explanations disguise how difficult this is to do.
This is the original use of the internet- giving away free knowledge to people, perfectly suited for the medium of a website.
While I do agree, if the author is reading the comments one piece of feedback I have is the overuse of the phrase "In this article I will...". It's a bit of a pet peeve of mine, and they use a version of the phrase three times in the first four paragraphs.
The combination of straightforward explanations and clear diagrams reminds me of David Macaulay's The Way Things Work which is one of my favorite books.