I think Lost is a good show. The writers aren't idiots. There's no way you can sustain interest in a mystery for five years. I think they realise this. So while it's the mystery aspect that gets you initially hooked and it's not something that you can truly get invested in, that's why they focus on the characters, because ultimately that's what people care about. It's the characters that you root for, that you invest in. With that I think they do it quite well.
Saying that, I'm not sure how bothered I would be by any of the characters dying, but I'm an odd duck.
I must say though, I'm actually starting to really like Jack. TV now, seems to focus so much on the rule breakers, the badasses, too much I think. I find Jack's nobility to be quite refreshing, even if it makes him do stupid things at times. More and more I'm beginning to find that interesting.
Characters like Sawyer, and Locke, whom I loved in season 1 are starting to bore me, in fact annoy me at times.
And I'm liking Sayid(or however it's spelt) a lot more. It's true, he seems to be the only one that asks the right questions, and knows what should be done. Pity he doesn't seem too get much screen time.
Desmond is pretty interesting too.