I knew the ending of "Sixth Sense" about 20 minutes into the film.
I'm a lot dimmer. Didn't get it until I was supposed to, although in retrospect it should have been obvious even to me.
I don't fin Shyamalan scary at all -- more creepy and far too slow. "The Sixth Sense" is the best of the three but once you've seen it, there's nothing to conjecture about,other than whether one believes in spirits or not. That it was almost immediately copied in "The Others" is sincere flattery.
No, I didn't get the ending on "The Others" either. In fact even now, although the surprise ending is the same, I don't find the two very similar. "The Others" is more of a classic ghost story, while "The Sixth Sense" is charting somewhat new territory.
I agree that Shyamalan is not particularly scary, although there are a few jumpy moments in both "The Sixth Sense" and "Signs", but I do find his work suspenseful, which is how I feel about Hitchcock as well. I think "Unbreakable" is Shyamalan's best film, but I am hesitant to recommend it to people for the reason you stated- the pace is daunting unless you are caught up in the story, which, being raised on comic book heros, I was.
"Unbreakable" is the one I have added to my collection, being the least dependent on the ending twist.