sloppy work
You obviously know what you're doing, seeing that you've used guidelines and whatnot...
the thing is, you don't really follow your guidelines and despite having them, your drawings turn out to be unproportional. practice more to get the details right. It seems like you're completely aware that you're not paying attention to getting the details right and just using them to get the point across. In my opinion a well-done tutorial should focus on the graphics of what it's trying to teach (it's a tutorial - a teaching tool - you don't want to teach sloppy work).
I like how you did the smaller stuff though like eyes and mouths etc.
Also don't draw on the computer unless you have a Wacom tablet. Drawing on the computer is bad for your wrist *and* the results are generally half-presentable. Kudos on the music though.