IMHO, Lost was the best new show on US TV last year. I've seen all of season one. There are some great episodes. The writing is excellent and it does some good character examination and interaction. As you go through the season, each episode seems to have one character as its main focus. There is a lot of "back story" --told from before the crash -- on the main characters. Each episode might answer one question that was previously left open, but then will open like 5 new questions. If you like the first couple episodes, you will probably like the rest. If you didn't like it, the rest is more of the same kind of thing, so you probably won't like the rest either.
I also like that there is multi-cultural/nationality cast. There aren't that many other shows that have that. Quite a few people from the US on there, admittedly, but that was where the plane was headed. Realistically they probably should have more Aussies.
Yeah the story lines are a bit fantastic (as in out of the ordinary), but it starts out that way so you don't feel like it is untrue to itself later in the season when the story lines are still that way. The season finale was a bit of cliffhanger so I am anxiously awaiting season 2 here in September!