i thought this was really good. i don't usually like films whose only attraction is providing a convoluted narrative for us to piece together so we can feel smart about ourselves (the usual suspects comes to mind), but i think this goes deeper because it's self-reflexive, and probes our own fascination with such puzzles.
i though the 'science vs. magic' aspect of it was really interesting; the idea that self-sacrifice was the only way their magic could work effectively, and thus the only way they could try and preserve some mystery in a world that's becoming increasingly scientific and secular... that's why the specific period setting worked so well.
in fact, i'll hop on the 'would like to give a second viewing' bandwagon. i thought the first half was a little slow and clumsily paced, though i'm wondering if that was because i wasn't paying enough attention to the subtle details and clues ("are you looking closely?", etc.).