Concierge.com's insider take:

Don't expect to see the world's most famous chef dashing around the kitchen of this avant-garde spin on the fast-food restaurant. Ferran Adrià's conceptual presence, though, seeps out in the juice of a world-class hamburger and crackles through the nut sauce in a dish of roasted vegetables romesco. His attitude also colors Fast Good's cartoonish, Jetsons-in-polka-dots, semi-self-service interior. Sometimes Adrià's haute-fast concept works, as in the burger italiano, whose gentle bite of arugula, mushy tomato confit, and unusually restrained melted gorgonzola all display appropriate deference to the burger's luscious ground veal, forming one of the best-balanced sandwiches in the city. At other times the concept takes a tragic misstep, as when french fries are cooked in olive oil, rendering them, amazingly, both soggy and tough at the same time—and virtually inedible. No reservations required.

Read our exclusive Barcelona itinerary with Adrià and his brother Albert.