If LOST had one major problem it was that the show was so universal, so gripping, that people made it there own. The audience felt ownership of it. And, I think, that's where so much of the letdown came from.
The other problem is that the show came about during the internet age. People discussed the show like crazy. The show runners took advantage of that, and sometimes it backfired. You want to blame somebody? Blame that asshole who posted the screenshot of the fake polar bear from the first run of ads for the pilot episode.
If that person hadn't done that, Lindelof & Co might not have worried so much about the minute attention people were paying to their show.