Commonly known as "Gordo's," this is a local staple taqueria.
The Elmwood location (2989 College) is popular with high school students in both Oakland and Berkeley as well as UC Berkeley students. You can also see fire fighters and cops there as well as construction workers and pretty much everyone else.
There's also a location on Solano (technically in Albany), and a new location on Telegraph (2404 Telegraph). There are a couple San Francisco locations as well. They all have the same menu, though when the Telegraph location opened up, the veggies changed from the soupy, traditional taqueria veggies to slightly fancier grilled looking ones and that migrated over at least to the Elmwood location. The soda sizes are smaller there as well.
The Elmwood location is tiny- no bathroom- and often has a line out on the street. There are a couple of counters in the windows and a few tables. It is considered poor etiquette to save tables while you're in line. The Telegraph location has a few more tables and a bathroom.
Some people don't like Gordo's because of the ordering system: the first guy takes your order, gets the tortillas ready and then passes the order along to the next guy on the counter. In this game-of-telephone system things often get confused so it's a good idea to keep your eyes on your order. Many other people absolutely love Gordo's- it's a bit of a cult classic. One of the amazing menu options is the quesadilla. The tortilla is dipped in oil then grilled on the griddle. If you are a vegetarian, it's amazing- it's then stuffed with beans and rice (and cheese of course) and it's possible to tell yourself it's healthy because of the complete protein! Crispy tacos are also amazing- cooked the same way as the quesadillas. Definitely not vegan-friendly and probably only fake-vegetarian-friendly.
People like Gordo's so much that two kids from Berkeley who moved to New York opened Dos Toros there which has almost exactly the same menu (only a little more expensive and more healthy!).