I saw it last night and thought it was phenomenal!
JP's acting was incredible. To feel such pity and yet such revulsion for the same person was really unsettling. The physicality was really interesting, and the obvious distress at first with his laughter that faded to simply embracing it as 'the real him' was clear.
I don't think he killed the woman at the end. He wouldn't have emerged so clean if the footsteps were real. Plus the bloody footsteps seemed to go on a little long and were formed a little too perfectly. I saw it as symbolic of him leaving a trail of blood and death wherever he goes and loving every minute of it. Of course he may have strangled her (not sure that he's physically strong enough to have emerged unscathed with no defensive wounds though?) and the bloody footprints could have still been delusion.
I hadn't even thought the whole thing could have been a delusion! It's an interesting thought. I'd considered that everything from the ambulance was though. So he was just taken to Arkham (to the final scene) and his delusion was that he was rescued by a crowd of adoring clowns that see him as their saviour.
I'd also noticed that the interior of the hospital was different too, but thought that maybe it was because he saw it as, effectively, his heaven. Surrounded by people that understand (other patients), fed and watered so he doesn't have to worry about it, knowledge that this is the worst it's going to get and he doesn't even care. Everything was so perfect and white it just didn't seem realistic for that to be the real appearance in Gotham. But it was his paradise and the place he was desperate to get to, so the white effectively symbolised heavenly clouds as he skipped along.
I figured his hair went back to dark because he hadn't bleached it and only used temp dye that came out after a couple of washes, especially used over such dark hair.
There's still so much to think about so I'll definitely be seeing it again!