For me food in Barcelona is mostly about Sea Food and Tapas, and for both you can find plenty of amazing options. Besides the traditional Tapas, I also enjoy trying "new / fushion style" Tapas. So restaurants that serve small plates (so that you can order several small dishes to share), but not offer the traditional Tapas, but rather Asian or Italian or Fushion etc. style small plates.
One must visit place in my opinion is the Mercad de la Boqueria, to sample some food from the different stalls and from the small bars / restaurants and kiosques there. A favorite place is kiosque Universal. Nothing fancy, but fresh and really tasty sea food and grilled vegetables and mushrooms and a very busy and lively place.
I also like to eat in one of the small outdoor places in La Barceloneta. Not fancy places, but with simple tasty stuff like Gambas al Ajillo, and outdoor seating, a lively atmosphere and very cheap. Maybe not so much suited for a evening meal, but for a snack and sGome great people watching.
Finally, I like the Food Blog Migrationology a lot, and there are a few good vlog on Barcelona on Youtube https://www.youtube.com/results?search_query=mark+wiens+barcelona