Watched it tonight.
Hmmm...it's a very interesting movie. From a directorial viewpoint it's a technical masterpiece and has a unique rhythm which switches effortlessly between in your face and claustrophobic single shots to a more relaxed note during some of the more intimate two handers. The only issue with that is it can become quite jarring particularly early on in the movie.
The acting is absolutely top notch, and Keaton deserves the plaudits he's getting, he did very well at conveying the inner turmoil of the main character as fractured and conflicted yet funny and ultimately sympathetic. Emma Stone deserves a nod for making the most of a small amount of screen time with an excellent performance. With Ed Norton it's more of a case of art imitating life as he plays a 'difficult to handle' actor, so no great stretches there although he's also very good.
As for the story, I found parts of it involving and other sections where it meanders less so.
It's a film I admired, and yet I can't imagine every wanting to watch it again which may sound odd, but that's what I came away from the experience feeling.
I think it's fair to say that it's going to be very divisive and I would also imagine that a few people will simply dismiss it at pretentious drivel, which is a shame as that's something it certainly isn't.