I will pose a simple question.
Has he gotten worse with every movie or, inversely, has the expectations that you have become so stale and stereotypical that if he doesn't deliver gimmicky crap, you get pissed off?
Let's address each of his movies from the perception of a movie critic.
"The Sixth Sense" kept people in suspense throughout and related to the supernatural and brilliantly played against our very own perceptions of what we were viewing. He played the viewer along, allowing to form their own expected standards and then turning that around at the end. A well made movie with great acting all around.
"Unbreakable" was a comic book related story and as such Shyamalan framed every scene as you would expect in a comic book. This was very apparent on my first viewing and I had to tip my hat to the film-maker that he is just because of his exceptional use of props to frame the main characters.
Great characters, great development and a brilliant Ying/Yang movie which shows things to be in balance even when we least expect them to be. I thought this movie was superior to Sixth Sense simply because the acting was so much better.
"Signs" was a movie about purpose. Notice that each movie has a different "theme". I personally thought this was his weakest movie but the acting again was decent and there was more comedy in this particular movie. He also had his strongest cameo yet in this movie. An above average movie all around and because it delivered some cheap thrills, the masses loved it.
"The Village" was a movie about relationships in a manner of speaking but more so about how we would react in a world or situation of our own creation and to what lengths people would go to live that lie. It is a movie about human nature at its basest and was, after Unbreakable, one of his strongest efforts. The entire scene near the end where Brody dies was weak, but otherwise great acting all around and the phobia's he plays on are similar to what we experience on a daily basis.
"Lady in the Water" was, in my eyes, his cleverest movie. The fact it did not do as well commercially was people's expectations, not the actual product. The movie is different from the others he has made because he doesn't base it on human nature, but rather he attacks and exploits the standard stereotypical crutches that other writers use when telling their story. He does this and then uses it to tell his own, quite fanciful story.
The bond between people and the atypical hero are a common theme and he has his longest and best role in any of his movies in this one. Every character has a purpose and the movie shows how the people arrive at their goal/purpose in life and the trials and tribulations. Unlike "Signs", the persons purpose is demonstrated in a different way and the clever little story unfolds much like a bed-time story, which was the purpose. The hope that is brought forth in this movie makes it one of the lighter of his stories and I enjoyed it a fair bit.
There are undoubtedly going to be people who are reluctant to be open-minded and who will trash the simply because of it's pacing but.
If you go in with a formulaic view on how things are supposed to be, you will likely enjoy attrocious garbage like Spiderman 3 and similar crap like X-Men 3. If you are a fan of quality movies and story telling that doesn't follow the same stale formula, you will enjoy Shyamalan's work.