If I hadn't started watching the first season and got hooked, I wouldn't have made it through the subsequent ones. I really enjoyed the Jack vs Locke (reason vs faith) theme. The first season started off very compelling but then the writers got lazy and too free with the crazy stuff and didn't tie it all in so I think they lost (ha ha) a lot of veiwers.
The ending was a cop-out in my opinion. I would have had it slowly revealed that the story was a novel Hurly was writing and the characters were all people that were his caretakers in the mental hospital. That way none of it would have had to make sense and the ending still would have been chilling. The way they ended it with it being a form of purgatory for Jack didn't work for me as there were too many gaps in the logic.