I didn't watch it, but from what I got from cultural hosmosys is that it is a group of people who fell on an island, find some weird people and stuff going on while they try to survive, including a smoke monster and some time-traveling shenanigans, and it all ends badly. Not necessarily bad like "all die", but bad like "it is a bad series ending".
Again, I didn't watch, but what I heard about the ending (not telling to avoid spoilers for those who might want) I am completely out of interest in trying it.