There is nothing particularly exciting about Serrano. It is similar to Chipotle, Qdoba and other US burrito chains. The idea is that you choose each of the ingredients that goes into your burrito, and there are enough flavorful options available to keep even vegans happy (2 different types of salsa, corn, lard-free beans, guacamole, seasoned rice, fried onions/peppers, many types of fresh veggies). The prices were fairly high by US standards. My meat-free, dairy-free burrito was around 800 ISK (approx. $7 USD), although I think this was largely due to the fact that they didn't have a different price structure for vegetarian menu items.