We just finished a low-key but important character arc for John Locke. During the first season and half the second season, Locke was normally calm and collected. He had good reason to be. From the flashbacks we found that he had been confined to a wheelchair and led a rather pitiful life. His past was full of abandonment issues. His father betrayed him and the love of his life left him because of his father issues. His had a boring job, supervised by someone half his age. His pleasures came from fantasy - war games and phone sex. He had tried to go on "walkabout" to test himself and been turned down because of his legs.
Then he crashed on the island and found that he could walk. The island became his walkabout. He tested himself and found that he was everything that he had hoped. With noting but a hunting knife, he could kill a wild boar or make a cradle.
He found the hatch which hinted at new mysteries.
Then things got frustrating. Locke and Jack started having problems. Locke found that he couldn't trust Jack and both were taken in by Sawyer.
Then they inherited a prisoner calling himself "Henry Gale". Gale very subtly sewed a few seeds of dissent, asking if it was alright for Locke to make decisions without Jack's approval. Locke got frustrated.
Then came the lock-down. While Locke was trapped, Gale went through the air vents. The alarm went off then everything went back to normal. At first Gale said that he entered the code and pressed the button. Later he said that the hatch was a joke and that the system reset on its own.
This bothered Locke. In addition, he totally lost control of Gale. Rather than being Gale's jailer he now has to ask permission (which can be denied) to see Gale.
There was always the possibility that the hatch is a fake - nothing more than a test to see how long the creators can get someone to press a button. If Gale is to believed (a bad assumption) then the hatch is a fake.
On top of everything else, Locke was hurt and has to use crutches. He almost ended back in the wheelchair.
His walkabout seemed to be nothing more than a trick and he was back where he started. He left the hatch, intending to let the alarm go off and do nothing.
Then he talked with Rose. We learned from her flashback that she had been dying from cancer and was healed by the island. She reminded Locke that they both knew that the island heals. That part is no hoax.
The next time we see Locke his calm is back and he is reconstructing the diagram he saw during the lock-down. He believes again.
Rose and Locke don't know it but the island healed Jin, also. Prior to coming to the island he couldn't father children but now Sun is pregnant and swears that he is the only possibility.
Jack continues to shoot down Kate whenever she gets romantic. She thanked him for taking her along to meet with the Others. He replied that she was there because they didn't want her - they had her and gave her back. She still stole a kiss when they were both trapped in a net.
One of the show's running gags - whenever it looks like these two might start getting physical, something happens. This time Michael reappeared.
As leaders go, Jack is pretty poor. Kate withheld information from him because he kept her out of the loop. Hurley made the same complaint earlier. Add in the friction between Locke and Jack, Sayid working Gale over against Jack's wishes and Jack's failure at organizing an army and Jack's leadership looks pretty poor.
Several people on the island have had visions of one kind or another. Jack's dead father led him to the caves. Boone had a vision of his sister being taken by the monster. Hurley saw an imaginary friend from his time in a mental hospital. Shannon saw Walt talking backwards. The island may heal the body but it is tough on the mind.
Finally, the diagram that Locke saw showed six labeled hatches with a seventh labeled with a question mark. So far we have seen three hatches - Locke's hatch, a long-abandoned one, and a recently abandoned medical hatch. Do the Others know about Locke's hatch? Do they know about all of the other hatches? How are they related? There's enough there to keep the show running for at least another couple of years.