Some general thoughts looking back at my post two years later:
* I drew every cell with a sheet of paper and a sharpie and then scanned everything in. My living room was covered with all of the cells of this comic. If I did it again, I'd probably just use my drawing tablet. However, it worked out well being low-tech with paper because I drew a lot of the cells on vacation (i.e. imagine me drawing these scenes on a picnic table next to family by the lake thinking I was a bit crazy). Unfortunately, one unforeseen consequence of doing it by hand was that it became very clear that my handwriting was too hard to read, so I had to manually erase all the writing and redo it using a decent looking font. This took a lot of time. I had originally thought about using comic-sans but am very glad I decided to use the Marker SD font instead. You can see my actual handwriting in the "crib sheet" cell at the end. It was going to be way too much work to make it look pretty.
* I was most surprised by how many college professors use my comic in their computer security classes. Hopefully it helps the students.
* I tried to emphasize Rijndael's state matrix by having the stick figure guy carry it everywhere as a briefcase, but I don't think that came across very clear.
* Although I was inspired by XKCD's style, I didn't copy the critical part of a witty comment in the hover text. If I had to do it again, I probably would have done so.
Thanks for all the feedback; it's what encourages me to invest so much time in making posts like this.