Sat here reflecting. I think it was brought together very nicely. I'm a very nonreligious guy but i'm satisfied by that and think it could have ended in a lot more worse ways. I think the Islands purpose is to relieve people of their misery, Jack would have never met Kate, Sawyer met Juliet, Desmond getting off and back to Penny, Locke finding his purpose, Claire and Charlie etc. etc. If you noticed in the 'alt', all the people there were happy and Christian opening the doors at the end meant they could move onto their next life, the theory of reincarnation. Everything that happened in Seasons 1-5 happened. Everything that happened in the on-Island timeline happened. Everything that happened in the "no-crash timeline" was part of purgatory and the Losties getting back together before they are able to move on to their next life.
They come, they fight, they destroy. It always ends the same.
An obvious statement but if you remember down the log flume there are skeletons. This I presume is for the purpose of showing us that the Island is a loop. At the end Hurley says to Ben 'You were a great number 2' Ben replies 'You were a great number one, Hurley' showing that the alt is some time in the future, obviously when they are all dead and probably as a result of a LOST 2 happening, if you catch my drift.
This theory is futher backed up by the fact Eko and Ana Lucia are not in the church at the end, Eko resolved his issues while he was still alive, didn't need to wait for the others. Ana still had a way to go. Locke helped Boone resolve most of his junk, except for whatever it is that he wanted to say before he died. Which he probably did with his actions in helping Shannon find Sayid.
There is good and evil in everyone (as MiB stated), people can only leave 'limbo' once they have redeemed themselves, notice Michael and Ben are not there yet becuase they weren't ready to leave.