The beauty of a film like Sixth Sense is that the twist wasn't obvious, unless you knew there was one. There were subtle hints to the twist, which if anything made the film more interesting, as you could go through and watch again for what you have missed.
Since then though, a twist at the end of a film haas become such a cliche. What once waa an original idea is now being over used in many films, such as this one. So much so that both my girlfriend and myself had worked out the twist, without even knowing for sure that there was indeed such a twist. The subtle hints are now big neon signs, pointing at the fact that something is not as it seems. Its then not hard to put two and two together and get four.