I've been eating at Humberto's since 1987 (yep, 22 years). I probably eat there 2-3 times a week. I've had exactly one bad meal in that entire time (bad batch of rolled tacos, which is my usual breakfast there). The rolled tacos have plenty of good quality guacamole, the carnitas are good, and the carne asado acceptable. The burritos are big and filling (and aren't filled up with rice, beans & salsa fresca like other places - here, you actually get a good quantity of meat). I usually can get two meals out of the burritos. Salsa verde is a bit watery, but it is home-made and picante, unlike some other places. Cops, fire fighters, city workers, vatos and students all stop by. The service is friendly and efficient. I also eat at a couple of other taco shops regularly, and still prefer Humberto's. The food here is better than at any of the Mexican restaurants in Old Town, although the selection is obviously limited. The decor is nothing to get excited about - Formica benches and tables, but hey, it's a taco shop folks.
Pros: Consistently good food for a taco shop.
Cons: Hey, it's a taco shop....