This place costs far, far too much. Sure, good presentation, decent enough food, but it's just way out of line for what it is and is targeted at tourists with deep wallets and little clue.
The staff are definitely less than stellar. None of them are local or even Spanish which shows owners that are trying to skimp as much as possible to maximize profits. They don't care much about service other than pushing people through the very expensive menu as fast as they can.
For those unaware, midday lunch menus are a common item in Barcelona wherein you can eat a good, three course meal for 8-12€. That would be one of the few times to actually eat at Big Fish as it's a menu less than 20€, EXCEPT, it's not available in August or possibly other peak tourism times in order to squeeze more money out of tourists. Minimum per person for a three course lunch w/out wine, 40€ minimum.
The terrace, while pleasant gets blasted by the sun no matter where you sit and we had to move inside.
The wine list is an abomination. Spain and more to the point, Catalonia have fantastic wines. They only have four Catalan wines on the menu and the rest are cheap wines from all over with a huge markup (our bottle in stores is 8€, but was 22€ at Big Fish). Oh, naturally, there's the "classy" bottle of Cristal for 200€... On top of all of this, our wine was lightly corked showing improper storage.
Also, their website is worthless. Pretty and all full of Flash, but useless in all practical ways.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.