I don't feel like I watched the same Batman as some people here. I thought the tone of the movie was inspiring by the end, and Batman's arc was going from menacing vigilante to a hero that the people of Gotham to look to in times of crisis.
This version of Bruce has just been utterly subsumed in his quest for vengeance, it's what he calls himself until the end of the movie when he monologues about how he needs to become more. It also mirrors Selina's arc where he saves her from killing Falcone and she's ultimately better off for it, same as he is by expanding the scope of what it means to be Batman.
Farrell and Dano were highlights, but I feel like calling them grounded or nothing special diminishes what makes the characters work so well. Farrell's Penguin is still coming up in the Gotham underworld, so he hasn't had time to fully become the Penguin we were all expecting. But he also provided some of the best comedic moments in the film. Dano's Riddler was a direct foil to Pattinson's Batman: they're both orphans traumatized by their childhoods who become vigilantes to fix Gotham in ways that work outside of the bureaucratic systems in place. Riddler has a serious case of arrested development, as evidenced by his infantile-like tantrum when Batman rejects his notion that they're somehow partners. Riddler also provided some low-key humor like his aforementioned tantrum or his "Hey guys thanks for subscribing" livestream. He's also always two steps ahead of Batman and almost completely succeeded in killing off all of Gotham's major players in the finale.
I didn't think it was super realistic at all, it felt like a nice pastiche of crime noir, superhero camp, thriller, and melodrama. I like that Gotham has this anachronistic feeling, where if you ignored the computers and handful of cell phones seen in the movie, it could feasibly take place in any time period.
And lastly, where is everyone saying this movie was ultra grim and lacking any levity? Gordon and Batman were always playing off each other, lots of visual gags like Batman eating poop after escaping the police headquarters, all the comedy was derived from character interactions and clashing personalities, not quips fired off with a big Marvel pause so the audience can do their laugh track.
Overall I loved this movie and plan on seeing it again.