The problem with twist endings
On paper, it's a good idea, give the audience something completely unexpected at the end and leave them wondering what the heck happened, how could they have misinterpreted everything so much and what the heck did they watch.
However, the problems arise immediately, when a movie is based on a twist. The rest of the movie isn't going to either make sense or seem very entertaining, because the moviemakers rely on the twist so heavily; the twist shall set you free!
Look at other movies with twist endings, and think how they would work WITHOUT the twist; most would be boring, incoherent, irrelevant messes, only SAVED by the twist at the end to elevate them into 'interesting movies'.
Now, there are some movies so heavily layered with tricks that even removing the twist would still not change that much - but removing ALL the tricks would reveal how boring the story really is, even with the twist..
(Memento, I am looking at you - watch Memento chronologically, and you'll see how stupid Leonard is and how boring and linear the VERY simple story really is (no wonder they needed all that 'Sammy Jankis-filler', that's then rendered completely irrelevant anyway) - there were some Fight Club-esque 'quick shots' that you might miss on the first viewing, like Leo shown to replace Sammy in some scenes, in the mental hospital 'recognizing' people and screaming 'test this, you quack!' - when he flips the bird, ONE of those shots has clearly Leo's hand and shirt, and so on)
The problem is that SO MUCH of the movie is necessarily rendered redundant, irrelevant or pointless - or possibly 'just a bunch of lies' or 'things that never actually happened that way', so why would you NOT feel like you wasted your time watching it?
A twist ending is like 'it was all just a dream'-ending, which DESTROYS any point of the whole story and renders 90% (or more) of the movie IRRELEVANT even to its own story and world.
Now, if done well, it can actually elevate a movie (Fight Club is a good example), especially if the movie doesn't END immediately after the reveal (Fight Club, again, keeps going for a good while after the reveal), if seamlessly incorporated INTO the story, it can serve as a magnificent shock, while still keeping the story relevant and intact (The Empire Strikes Back does it perfectly, although raises many questions about íncest and why Vader doesn't sense his own daughter despite extremely close proximity in multiple scenes, including TORTURING HER (which has zero effect on her for some reason))..
The problem with twist endings is that often it's the ONLY thing the movie has to offer, but the audience has to WADE THROUGH so much irrelevant boredom to get there, it's not even worth it anymore.
It can be done right, but usually it isn't, and "Primal Fear" suffers from being an incoherent mess that only 'works' because of the twist at the end that kind of kills most of the point of the movie. I guess it has a 'poignant message' and punches the ego of a smug lawyer, but that's about it.
Twist ending-movies are often not very entertaining without the twist - remove the twist and what have you got? Usually nothing worth watching. I wouldn't watch this movie again for the entertainment value, because it has almost none. Norton's performances are great, but I am sure many actors could've pulled off that stuff. Look how well Brad Pitt plays a 'crazy character' in so many movies, he's absolutely brilliant.
A badly done twist movie doesn't offer more than the twist, so the rest is basically 'filler' you have to wade through.
In my opinion, it'd be better to make a movie that just tells a GOOD STORY, and not build things around a twist, but I guess I am in the minority..