[laputan_machine]

This looks nice but is telling you what to do, instead of giving you problems to solve. I don't think this is a good method of teaching.

Edit: After lesson 8 you start to get problems to solve

Edit 2: I take it back, this is the first time I've understood how lookarounds work. Great stuff!

[Cthulhu_]

That's what it starts out, then it tests you with some problems to solve based on what you learned before.