I just had a glance at the first two lessons. Seems to be quite detailed... maybe a bit too detailed in fact. I mean, sure hexadecimal is important, but does one need to know how to change bases and how data is represented before he writes his first hello world? I think not. I would have kept that for later, and gone straight to the code.
You really have to give the reader what he is waiting for to keep him interested, even if this implies shuffling your chapters a bit or even coming back twice on the same subject.