We can talk all day about how disappointing individual character stories were. For me, though, it's the central conflict that ultimately ruins the show. Once everything is revealed, absolutely nothing makes any sense.
I haven't watched Lost since it ended so forgive me if I get any of this wrong.
So, way back on Across the Sea, a crazy lady is guarding whatever the hell the heart of the island is supposed to be. She murders someone and steals her children, MIB and Jacob. MIB grows up wanting to leave, but crazy lady is crazy and murders a bunch more people to prevent that. MIB responds by killing crazy lady. Then Jacob, instead of just acknowledging that their fake mother was crazy and kind of had it coming, instead of just letting his long-suffering brother leave this prison, he... throws MIB into the heart of the island? The very thing Jacob was supposed to be protecting? This creates the smoke monster, and now MIB can't leave without ending the world.
So right away this is stupid. Good job Jacob, you created this entire problem by being a moron. Luckily, even though you apparently can't kill MIB, he also can't kill you! And no one can even find this magical teleporting island unless Jacob allows them to. All he needs to do is accept his fate and keep MIB trapped forever. Instead of doing that, Jacob ruins countless lives across hundreds of years by bringing people to the island.
MIB, meanwhile, needs to convince one of these people to kill Jacob. And look! An airplane full of new people have just crashed on the island! Does he go and talk to them and manipulate them in any way? No. It's much smarter to spend the first few seasons harassing them randomly as a smoke monster, even killing several of them for no reason.
Like, this is what I mean about the entire show being retroactively ruined. Nothing that Jacob or MIB does at any point makes any sense. It's hard to get invested in individual character stories when the overall conflict they're a part of is this shoddy.
**R.O.B.A.Z.O.I.D** (On mobile)