The full-service restaurants around the World Showcase Lagoon break down into four groups, IMHO: The truly superior restaurant (Chefs de France), the excellent restaurants (like Le Cellier), the decent restaurants (like Biergarten), and the terrible restaurants (like Nine Dragons). IMHO, San Angel In fits into that second-to-last category: It's decent, but nothing to write home about, and for me, dining at full-service restaurants is all about having something to write home about.
More specifically, while some of the food is yummy, it's not consistently the case for the entire menu, and nothing is really amazingly great. They make a good play at providing atmosphere, with the river and the volcano, but overall, it is just plain too dark to enjoy the meal. No, it's not "romantically lit" -- it's dark. Great chefs will tell you that you eat with your eyes, nose and mouth, and with as dark as they keep the place, you're missing out on 1/3 of the dining experience. Service was good, but again, nothing to write home about.
YMMV.