I didn't like it.
That's to say, I'd give it a 3/5 because you can't really argue against the thing that do work here (often also the thing working against it), but when it ended I was left with the oldest question in the universe, what's the point?
Because there doesn't seem to be any, or maybe there is, buried somewhere under the self-absorbed insinuations, implications and imaginations that are the trademarks of Inarritu's ever growing pretentious career. If you thought he couldn't outdo Babel, think again!
And that's my problem with it, there's a movie here that works, and then there's everything that doesn't. When the movie begins, the meta stuff with Keaton's and Norton's characters being exaggerated versions of themselves is kinda funny, as well as the occasional fourth wall breaking like the street drummer playing the soundtrack to the movie. But then it goes on and on and it just becomes increasingly self-indulgent, a movie overly pleased with itself for how elaborate it believes it is
But in the end, what do we have? A story we've really seen many times before, with the cliché ending to accomodate it. Acting performances that know one highlight in Keaton, a couple performances played too self-consciously to be truly great by Norton and Watts while Emma Stone proved to me once again that we've long seen the best she has to offer as an actress, and it really isn't that much.
Camera work that seems like it's impressive but serves no purpose and strangely, often falls flat. To me the tracking shot is the ultimate form of showing off in a movie, to boast your impeccable strength as a filmmaker by staging the most complex situations imaginable, and then play it out in a single take. But if you don't have anything to show off, again, what's the point? This is a two hour movie where at least 90 minutes are dialogues, so a lot of the shots start with a camera entering a room, a scene plays out, then the camera moves out. Rinse and repeat, with little to no variation. The truly impressive shots can be counted on one hand, like the big Birdman blockbuster hallucination and Riggan's underwear journey on the street that ends with him getting back on stage.
But a worse offender is that the cuts become more obvious as the movie goes on, and the "one long tracking shot illusion" gimmick starts to work against itself. You aren't supposed to 'notice' cuts, that's the whole goal behind editing. This concept often only works when things are so hectic that a 'shift' isn't that noticeable (see Children of Men and True Detective's copy/pasted action filled "tracking shots"), but like I said, here so many of the shots are alike that each cut moment is right in front of you, and I actually started to think this would've worked better if it was cut up a bit more. That's not to diminish how technically impressive the camera work in the movie is, but in the end it more often feels like an extensive gimmick than something that truly adds something to the movie.
What we're left with is an experience remarkably empty for a movie filled to the brim, possibly because it all adds up to a whole bunch of nothing. The best made failure of the year.