So yes, has his career become laughable in relation to his inability to make any movie that isn't that different from The Sixth Sense - yes, most certainly. However, as an example of someone who has been successful creating movies that predominantly revolve around plot twists, it is actually a very good example.
Plus, the Sixth Sense was actually good the first time I watched it.
I say laughable because a better example would be someone who had continued success ;P Shyamalan is a laughing stock at this point, a "1 hit wonder" if you will with the Sixth Sense, which yes was a good film. Yes I know Signs was a success also, but I personally felt Unbreakable was a better film despite it not having anywhere near the success and Signs was grossly over rated.