Favorite LOST theory:
That Jack dreamed the entire show while he was lying delirious in the jungle dying and all the characters were just people he had seen on the plane who his mind created back stories and even names for and everything. Which would make sense in a way because a lot of their issues did mirror his own - issues with parents and the struggle for control within chaos and then that would be how he got to fulfill his own deepest longing with needing to fix everything and save everyone by being Island Keeper. This would explain why there were so many things that felt like plot holes and unanswered questions. Also, I like the idea that each character maybe represented a different part of Jack's psyche. Kate killed her abusive dad, maybe part of Jack wished he had...Charlie was addicted to heroin, Jack was addicted to pain pills in the flash forward so perhaps he had been before...Hurley and Libby were in the psych ward, Jack exhibited a tenuous grasp on reality when he became obsessed with his ex wife and thought she was sleeping with his dad. Etc. Etc. It would also explain why so many names were so symbolic.
I know it's a huge cliche, but (as ex-psychology major) I love the idea of the unconscious and how different issues are played out there and what different people might represent etc. etc. Like in those episodes of Buffy and Charmed, where reality became kind of a question, and ultimately Buffy chose to stay in Sunnydale reality but it was still left open-ended as to whether that actually was reality.
Anyway, I don't actually believe this theory at all, or that it's what the writers intended and it would have pissed off everybody if that had been the ending, but then I feel like the way they ended it, intentional or not, did leave that potentially open to interpretation, and it's just something fun to think about. The plane going overhead could have been just another plane, as the Oceanic could have crashed on some not so desolate island in the middle of nowhere, just an island.
So, I guess that would be...my theory (I mean some of the specific details, at least)? My theory that I don't believe in lol
Then again, the people who did hate the finale...would that have been better or worse??