I cuss you bad
Very late reply in this, but I think this is unfair. There's the saying that everyone has one masterpiece in them. Shyamalan actually got to make his.Here's the twist... The Sixth Sense was a fluke!
The Sixth Sense is an absolute masterpiece. It's a really personal heartfelt film, with clever cinematography, that tells two stories that work different ways in second viewing (and a different protagonist the second time) and with truly brilliant performances. It changes genre a number of times and still feels coherent. It's fundamentally impossible for somebody bad at directing to make something that does something that audacious and actually pull it off.
Unbreakable is also really, really good. Signs is excellently directed; if it weren't for the incredibly dumbass twist people would be seeing it for the masterpiece of tension it is.
I don't know what happened to the guy. His early films were marred by him having to add a twist and the compromises you have to do to set them up make the films worse. Even more silly because you go into an M Night Shyamalan film expecting one, so he has to go even more gonzo to surprise you. I wish he'd mentally settled on "a Shyamalan film is bloody excellent" rather than "an Shyamalan film is a magic trick"