It makes no sense to say it was all "in Jack's mind." The whole point was that what is important are the relationships you have with people. The church scene was a reuniting of all of these characters. Why would Jack's big after-life reunion be with a bunch of people he imagined?
IMO, What happened on the island happened. As the various characters died, they entered the afterlife. They were all stuck in a world created collectively and needed the help of each other to move on, the point being that their time on the island was the most important time in their lives. In fact, their time on the island is what gave their lives meaning at all. They needed each other in life, and they needed each other in death.
I agree, from a storytelling standpoint, this was a little strange. It did in a way trivialize the events of the show. But, then again, the events being trivial was sort of the point, I think. There is something more than our daily struggles and what not, no matter how earth shattering they seem. Might be a little cheesy, but no more than anything else in this show. This show is flawed, sure, but I think some of you guys are over simplifying this ending a bit. All things considered, I give it a
