Watched this last night having been meaning to watch it for the last two months. In short, it's a beautifully shot film and I would agree that it renders the 1950s feel really well. The performances are well-delivered and suitably balanced for the "both sides of the coin" element of the story.
However, the film was one big cock tease. The score and sound effects throughout the film were effective in maintaining tension, but invariably led nowhere. For example: haunting strings on the approach to the asylum, reaches a crescendo and... ummmm... a nice garden with people planting flowers. I 'get' what that achieves in terms of making the viewer unsettled, but done repeatedly, it really set a precedent for the ending in some ways - lots of tension that, sadly, sort of fizzles away.
It's also quite convoluted in places and seems to get trapped in its own internal logic. I suppose one might suggest that's a defining quality of psychosis, but it's to the detriment of the story being told. There's a slight absence of clarity of purpose in certain scenes which (although it may argued was a requirement for the film's central themes) led to what appears to be some awkward editing in post-production. I don't feel like they captured on film 100% of what they needed to tell the story well. Being confusing or ambiguous doesn't necessarily equate with intelligent film-making.
That said, it's about a million times better than most of the thriller/horror films that are pumped out these days. It's actually a very good film and probably well worth the time it demands for a second (or third) viewing... but it just lacks a certain amount of coherence in places that would have elevated it to something else.