This review from Erin Lindsey, who does the webcomic Venus Envy, captures my impressions from the FG presentation of Mirromask fragments:
Go see MirrorMask. Go see it right now. It's like Neil Gaiman ate 'Labyrinthe' after covering it with too much taco sauce, went to bed with an upset stomach, and dreamed it even MORE awesome and weird (and without David Bowie, to boot). Plus it has the world's hardest riddle, which I won't spoil just now.