I have yet to read Como Agua Para Chocolate, but I didn't like the movie much. I felt like the magical realistic theme of the book, from what I got from the movie, didn't translate well on film, but would be fantastic in literature.
I totally loved that book. I agree with you about the movie because our ideas of how magical things could be are always better than someone else ideas (in this case the filmmaker’s). What I liked the most about Como agua para Chocolate was the idea of Spontaneous human combustion, the craziness of Tita’s mother even after death, and the idealization of the sister that runs away to make her independent life.
I also found very erotic and sad the description of how Tita made some of the recipes, and their consequences were very funny at times, like the one where everyone ends crying or that other were everybody become part of an orgy.