Basically, the first series made some sense (except the black smoke and the weird kid who read about stuff, which then always appeared, for no explained reason).
After that, it stopped making sense. They had to push a button every 108 minutes to save the world, then decided they couldn't be bothered, and the world almost ended, then they turned a key and the was a big light and then they didn't have to push the button anymore. Then a boat came, so they moved the island, dislodging it from time. They all jumped about in time a bit, then eventually all met up in the past, and set off a bomb in the middle of the island. After that, they all came back to the present, Hurley took over from Jacob as ruler of the island, changed the rules, and then everyone died and met up in a church.