The flow of the site immediately sticks out in a great way. As a user the navigation bar for the lessons is easily understood.

Each lesson has its own key terms that can be used as a mini nav within the lesson which is helpful.

The code layout is simple and not overwhelming. Its nice to see long hand vs short hand

People can argue all day long about the right content but this seems to be a great start. Clearly the author has put much prep and time into considering this.