Well, I tried to rework it while thinking about tetris pieces, but I'm not sure it's really an improvement
:
But, in all seriousness, thanks for the edit (and no worries about changing the shape; I'm not exactly an expert on skull anatomy). I think I understand a little better, at least. Here's my latest attempt:
The most obvious difference I see between yours and mine is that mine still has some single-pixel irregularities breaking up the lines (e.g. along the shadows forming the brow, and on the upper lip). When I remove those, it looks too smooth and, for lack of a better word, plasticky compared to the effect I'm going for. Is there a better way to suggest irregularities while still making the shape clear? Or am I just overthinking this whole thing?
(just for fun, I recolored the tetris-ified one:
I'm not really sure why. I spent way too long on this stupid joke, anyway...)