These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Memetic Mutation: The distinctive way the title character shouts "Biiiiiiiiird-man!" at the end of the opening credits.
Alternate Character Interpretation: Riggan's Birdman persona. Is he a malevolent presence that wants to torment Riggan? Or a gruff voice of reason meant to help Riggan by telling him the truth and boosting his ego?
Award Snub: Although the film was nominated for 9, tying The Grand Budapest Hotel for the most nominations, it received no nomination for Film Editing, which is strange considering how it's one of the most distinctive aspects of the film's style.
Some felt that Michael Keaton should've won for Best Actor at the Oscars after he lost to Eddie Redmayne for his role in The Theory Of Everything.
Critical Dissonance: In fact, as of its win at the 2015 Oscars, Birdman was the 2nd lowest-grossing Best Picture winner of all time. The only one that grossed less was The Hurt Locker.
Fridge Brilliance: The entire movie is made to look it happened in one go, just like a stage play.
I was wondering how Birdman can use his wings to fly when they're clearly part of his costume. Then I remembered Riggan's telekinetic tantrum and it all made sense: Birdman can control his wings with his thoughts. If his powers are thought-based, then a comeback movie involving a 60-year-old Birdman might just work.
He Really Can Act: Despite losing the Oscar for Best Actor, there's no denying that Michael Keaton delivers a stunning performance after nearly a decade of mediocre and secondary roles.
Signature Scene: The scene where Riggan walks through Times Square in nothing but his underwear.
True Art Is Angsty: The movie depicts how the world of Broadway is embracing this trope. Riggan's suicide attempt is the icing on the cake.