I found it bold and great that the film started with her masturbating in the bath (which is apparently a daily ritual), and this also neatly foreshadowed the abovementioned scene.
Could have done without the flight of fancy into blackandwhite singing/dancing, also.
Perhaps the most del Toro moment, and something I literally gasped at, was where her scars turned into gills. That was amazing.
All in all, a tightly told story with gripping visuals. I'm also reliably informed that half of Tumblr wants to fuck the fish now.