Well I had very mixed feelings:
I loved the spiritual/philosophical resolutions created in the "sideways" afterlife. The reunions and re-connections were emotionally satisfying. If the texture of the whole series was at least primarily structured as a spiritual journey, this would have been more than enough for me ... but, as the complexion of the show had also integrated a tremendous amount of technological science fiction-based intrigue, I felt that overall the result was especially disappointing. This is what happens when you take the science out of science fiction, i.e. you get fantasy. I love fantasy, but this product was girded in aspects of both sci-fi and fantasy, I thought rather successfully, until I realized with this "televised finale" that the writers had in fact exceeded their grasp of the first aspect and more or less "ran to momma," totally embracing a quick fix in the latter (thereby ignoring any further creative work with the technical fun of the show). I think they decided to take a vacation from whatever they were getting paid to do, without fulfilling their implied contract to the science-fiction fan-base, whatsoever (while simultaneously avoiding further criticism of their craft as "science-fiction" writers). Many of us who were lured into spending our evenings watching this particular TV drama were, I believe, entertained on both levels, only to find that Lost's creative team had in fact simply been making up a number of things purely for the sake of ratings, without any serious commitment to their craft as art. These guys weren't "jumping the shark" so much as they were bouncing off the tops of many sharks on an ongoing basis! Of course, most of the people who worked on this project (especially those with royalty benefits), have fully succeeded in achieving the primary goal of any working professionals, that of making money. The financial futures of Lost's creative team are set with the implied notion that they have, in a way, made off with the jewels, i.e. left the premises with those "as yet" untold stories that might continue to lead us further down the rabbit hole, where science seems to mirror fantasy, on an island that can move through time and space (with a simple turn of the screw). All I can say is make way for the sequels, and many more shows riddled with unanswered mysteries...
Doubt my prediction? We the "science-fiction" fans of Lost would still love to know why:
The nameless woman who raised the "man in black" and Jacob had to kill their mother, why she was immortal, where she came from, how she came to the island, and why she needed to protect "the light".
A simple turn of a wheel placed in the well by the man in black (or his people) can make the island disappear or jump through time.
A simple push of a button can stifle an electromagnetic "geyser" capable of pulling aircraft out of the sky, only to by cancelled out forever by the detonation of a nuclear bomb which itself does not destroy the human that deploys it firsthand (unless you're Juliet, of course).
A megalithic statue of the Egyptian god Sobek (with only four toes) became the refuge of an "immortal" Jacob until his knifing death at the hands of a mere mortal, while Jacob himself was sired by a shipwrecked survivor of the Roman Empire.
A light emanating from beneath a stone pool can be snuffed out when a stone cork (remarkably light, despite its size) is removed only to be rekindled when the same stone cork is replaced.
The light (or energy) at that same pool had the ability to transform an immortalized being into a shapeless predator that can mimic any dead human form (and/or kill without mercy), yet only render "unconscious" the survivors Jack and Desmond.
A "given" cup of water from the creek exiting the pool can somehow make a person a protector of the light.
Women who become pregnant on the island do not survive their childbirth.
Finding the island (and departure from it) is somehow impossible except by way of air travel, submarine or shipwreck.
An airborne "shape-shifting" life-form cannot escape the island while "man-made" aircraft can.
Have I left anything out?
Many of us have speculated that the island is a crashed spacecraft or space station with either extraterrestrial or distant-future origins, that has somehow morphed into the terran landscape. Wouldn't it be ironic if our guesses were a little too close to what the creators had in mind, and that our intuitive blogs have somehow intimidated the creators into sneaking off with their own booty...