The problem with Lost isn't the bad writing, silly drama, forced love triangle, or all the things designed just to waste time. The problem with Lost is that it's dishonest. Almost every moment of the show implies that there's some revelation that will explain all of this, some answer to all the questions.
Unfortunately, the majority of questions were red herrings, and the answers we do get are "a wizard did it, hundreds of years ago". This is not satisfactory.
One of my largest irritations with the show is the way the release of information is artificially regulated. All new characters are implied to have knowledge beyond our comprehension, only to reveal a few trivial facts before admitting that they, too, know nothing of any interest. Why does everyone act so unbelievably mysterious and secretive when they don't know anything worth hiding? Everyone new is implied to know about the island. They end up knowing that "it's magic". It turns out that that's all there is to know, but that isn't enough information to hide. In fact, it's not really information at all, since magic in Lost is the worst kind of magic, the kind that has no rules whatsoever, that inhibits some things and allows others, for no apparent reason. The sort of magic that gives endless red herrings, but never leads to any answers.*
Even worse than the regulation of information is the fact that no one actually had a reason to be secretive.** There's no conspiracy, no oath of silence, no reason for any of the major players, (Ben, Richard, Jacob, or Flock) to not walk out of the jungle the day of the crash and ask for assistance from our protagonists. The only reason they hid in the jungle all this time is because the show wouldn't be very dramatic if they didn't. I'm not saying drama is bad, I'm saying drama should be justified by the story. It's a standard event in Lost for characters to announce "we don't have time to explain [question X]", then walk through the jungle for hours, presumably unable to talk because they're walking so hard. Giving the show the benefit of the doubt, I always assumed characters didn't want to say anything because they were holding some secret. It turns out the show literally wants us to believe that characters didn't tell each other things for years because they didn't find the time***. They must do a lot of walking on that island.
Another issue is the way character takes a backseat to pointless conflict and forced plot progression. The most common way for a character to decide something is that it's "fate". Maybe it's just me, but "fate" is the most disingenuous way imaginable to justify something. There's no way a character can tell if something should or shouldn't be done using "fate". "Fate" may as well be replaced by "The writers needed to get to the next scene, but couldn't imagine a motive to do something so unreasonable or dangerous to get the characters there." It's funny the writers can't find time to justify anyone's actions, but there's plenty of time for characters to dodge questions about motive, and the increasingly obnoxious flash backs/forwards/sides.
The central lie of Lost is that it's a puzzle, one that can be pieced together by the astute viewer, and one that solves the problems. The Penny Arcade guys talked about this on their podcast, justifying their abandonment of the show. Basically, when the show gives you some data, there's no chance that it actually applies to any of the questions of the show until the last half of the last season. Everything that happens until then is just wandering around with characters who know only slightly more than us. If Lost is a puzzle, it's one where you get only a couple pieces, then it turns out the picture is just "IT WAS ALL MAGIC" in magenta letters. It's a stupid answer, and it's not one that justifies the time that the fans have put into it.
*There's also magic that works outside of the island, (The Numbers****, Walt****, Jacob, etc.) so it's not even clear how the island special in the sense of being magic, since magic is works away from the island too.
**Think about it, there's information people have that they are unwilling to give out at one point, then later they'll just offhandedly mention it because the audience already knows about it. (Recent example, Flocke blandly mentions that he used to be human, when he wasn't even asked in the second to last episode, when in earlier episodes he refused to even answer Jack directly asking "what are you?" There's no reason for him to not answer Jack then volunteer the information later...except the audience knows already.)
***Actually, it could be because in Lost, you're only allowed to ask a question once. I know it wouldn't be very dramatic if people just asked the same question all the time, but there should be a reason why people don't come back to asking the important questions other than dramatic necessity and keeping information from the audience.
**** Although it seems the writers forgot about these, so maybe they don't count.