I agree that people are a bit harsh on this place. It's a Canadian burrito joint after all, and a true Mexican Restaurant would probably not have whole wheat tortillas, brown rice, and lowfat sour cream. On that note, I think Z-Teca is a good place to have a meal before sitting in class for 3 hours. I love their industrial chic seating area, great for getting last minute homework done. Prices are great, especially as it seems to be the trend to overcharge for healthy food.
I have been pretty satisfied with the grilled shrimp burrito (light and delicate), though I will admit their chicken is on the bland side. Their food has a very clean and healthy flavour with very little aftertaste.
I've never been to Chipotle, which this place often gets compared to. However, I just got back from a week of taco binging in Mexico City and the fact that I am not complaining about Z-Teca is probably not a bad thing.