There's quite a big difficulty spike so to speak in the later section as you go towards the code examples. The beginning explains relatively simple concepts like binary, then basically jmps into an instruction table which won't make sense to anyone who hasn't done some form of programming (they would know binary then, right?).
The tone is also a bit off putting, although I might be out of touch with today's teenagers. When I was learning asm as a teen I learned it from grungy 1337 h4x0r sites (well, they didn't actually use 1337speak except ironically, much like today) which were at least a great deal.. meaner? less nice?.. than the tone of the article.
From what I wrote I gather my main criticism is that it doesn't know its audience. However, it seemingly _was_ produced by an actual group of teenager as per the author's HN comment:
> Hack Club is a group of teenagers from all over the world, and we decided to learn assembly together from scratch and see what happened.
Although it probably means a trained adult was lightly helped by some teenagers in producing it.
I hope this didn't sound too harsh, the effort is very good and so are the illustrations. It needs some fleshing and perhaps a little less "yay!!". Learning assembly is not actually that fun, it's rather painful. It's what you do with it that is fun.