My plans got changed around and I never made it to Estimar, but I feel pretty confident that it's worth trying. Another place that I couldn't get into but you might as well check out: Berbena, which seems neo-bistro-y with an interesting-looking menu (lamb's brain, tongue, a relatively lengthy cheese selection).
A neo-bistro that I did make it to is Besta, which has Galician and Catalonian influences. Pristine razor clams and other small plates all under 25 euro (tasting menus for 55 and 75), and they make their own gin and coffee liqueur. It also happens to be around the corner from Gresca, which you might know as it's been open since 2017. If you don't, it's a fun open-kitchen wine bar with simple but sharp cooking. The Besta people also have a seafood-focused restaurant called Batea that opened last year.
I'm having trouble finding out how old it is, but Lluritu in Gracia is great for simple, perfectly grilled seafood. Also in Gracia and seafood-focused (though slightly less simple -- think scallops and pork belly with herb oil) is Hermós Bar de Peix, which opened over the summer in the Mercat de la Llibertat. It's run by the same team behind the neighborhood's popular La Pubilla and Extra Bar.
Agreste de Fabio & Roser is an Italian-Catalan restaurant way out behind Park Güell in what feels like the middle of nowhere. It took over a former autobody shop and has pretty outstanding, polished cooking and service, plus a deep wine list. There's an 80 euro tasting menu or a surprisingly affordable a la carte (20 euro for a duck main course).
Have to say, next to Gracia, El Poble-Sec might have had my favorite restaurants. Quimet y Quimet for conservas, which is popular for a reason, but also Taberna Noroeste, a tasting menu-only joint with a good amount of Galician influence. The latter does two seatings (it's just two chefs and one server who is also the host and dishwasher). It's around 10-12 courses with plenty of wonderfully cooked seafood, a few standout meat dishes (lamb tripe with Swiss chard), and some incredible sauces.
I can't say enough good things about Casa Maians, a market-driven Barceloneta restaurant with a long list of daily specials and a menu of Catalan home cooking like red shrimp stewed with blood sausage and chickpeas, or pig's feet over saffron milk cap mushrooms and black-eyed peas, plus a number of fideuà and rice options.
Frankly, there wasn't a bad meal the entire trip. Putting Hisop on the list for next time. Bar Babula looks promising -- looking forward to the report.