I think the critics had a problem with it from a film theory point of view because it didn't build on the characters, often leaving them stereotypes to work with and unexplained backstories. You can't say that any of the characters have relevant depth. At least thats what I get when they say Shyamalan has no narrative cohesion which was arguably Sixth Sense's most notable point.
But from a perspective of a film-going experience, I can see see why I like it and why its advocates might have liked it as well. It is a bedtime story come to life which is why the overwrought scenes work. It's like something you might have daydreamed about after reading a fairy tale anthology. It's so visceral and in the moment for the greater part of the film, when you're on your toes to find out what he's going to pull out of his hat next. Maybe a witch? Perhaps a character reversal that was not hinted at? It does seem like a story he made on the fly which somehow made sense in the context of the tale.
It's also a beautiful picture that puts you right in the atmosphere of the apartment complex that it hardly departs from, imaginative angles and the intriguing dialogue is something I've come to expect from his films. He's also tried out humour this time round with the critical inclusion of Paul Giamatti which I felt was its biggest asset. He manages to switch between drama and comedy with such ease that his character is rightly the centre of the entire film.
I also don't see the big hullabaloo about Shyamalan casting himself as the future's intellectual saviour, he could have easily casted somebody else but its not like his acting ruined the film. He wasn't Sofia Coppola bad by any stretch of the imagination. It's a personal project for him, especially with the critic character's inclusion. It's an audible F**k You to those that can his films after Sixth Sense like they were the biggest creative flops ever made. If they failed to see some humour in that then they do deserve to get flipped off. Director's have egos, some have vast vanity projects, and people need to understand why thats interesting not insulting.
I really do feel like watching the movie again, I would think it'd be better the second time around. Like being told a bedtime story again and again or playing through an RPG again just because the glut of characters and mythos were so exciting the first time round.