Complete scientific explanations are great, and sure it would have been interesting to get a few more of those out of Lost, but the Island was NEVER what the show was about: it was about the people. Every moment of the show was about the people; how they reacted to the stresses they faced (plane crash, mysterious monsters, evil island residents, lack of rescue, pressing button on a short timescale, uncontrolled time shifts, loves lost, loves gained, etc, etc, etc.) Why do you think we got all the flashbacks/flashforwards/flashsideways!? The Island was just a strange, mysterious setting in which to put the characters and watch them react.
Personally, I love the fact we actually don't know what happened to Ford/Kate, etal. on the plane that did leave the island. According to Christian, they may well have gotten back to civilization and lived long lives. I love the fact that Ben was STILL conflicted, and even though forgiven, not yet ready to move on. I don't yet know what to make of the fact that Michael and Walt were missing, yet the dog was there with Jack at the end.
If a show answers ALL the questions, what is the point? Lost gave us something to think about long after the show has ended. I am grateful it was here, shining brightly in the current wasteland of mindless, idiotic, juvenile reality tv!