I also really love San Angel Inn, have been there several times over the past few years with never anything but a wonderful meal and service. I love the food and atmosphere and if we don't go, we always regret it!
All that said...
You are probably going to get a lot of very negative reviews from people who say this place serves up yucky, non authentic Mexican food, that the service is awful, the tables too cramped and to skip it. I swear, this place gets more heated hate on the dis than any other WDW eatery. And I respect that because I know experiences vary. But I always say go for it. Its not Tex Mex which is what the vast majority of Americans consider "true" Mexican food. Its dark in there but I like that, some do not. In the end you won't know until you try it, and while a lot of people don't like it, a lot of people like myself do, and they base that opinion on multiple visits. We all have different tastes! I also like to eat here at an off time to increase my chances of a lesser wait to get my table and get a table nearer the water. Because its hooked up to a ride, its visible and it gets a lot of walk ups so its frequently quite crowded.
I love their filet, their tortilla soup, margaritas and the atmosphere. Ask for a waterside table and tell them you will wait for one. It makes it even more enjoyable!