Yep. I get the idea the ending was thought of either at the end of season 1 or 2. Total laziness in writing. Or, Dharma, time travel just a smoke screen to cover their tracks(writers) so nobody catches on.
Because we all were into the characters and the mystery of the island and time travel and it was all for naught.
The ending was written before the pilot aired. It was originally just going to be a drama on an island, but in order for JJ Abrams to sign on, they had to go with a more Sci-Fi approach, and have a definite and more interesting story to tell.
The DHARMA Initiative is explained by the way. And Time travel was used by the writers to eventually get them back to the 70's and blow up the hydrogen bomb, creating the alternate timeline (purgatory).
And I understand people want to know what the island was exactly. I felt the same way. But that wasn't what the show was. The show was about the characters, which is why week in and week out if flashed back to their lives before the island was even known to them. The island, the DHARMA Initiative, Good vs. Evil...all of these were simply devices the writers used to make the show more interesting, and to allow for interaction with the characters.
"It only ends once, anything that happens before that is just progress."