I'm still very interested in Lost and it's still one of my favorites. Every now and then there's a weak episode, but even those have some interesting elements. Every now and then one of the back stories is also somewhat weak. I'm fine not knowing everything, but to keep people interested they need to wrap some details while introducing other plots before the series ends.

Lost has suffered a bit by not having as well developed a story line ahead of time as it could have. There have been a lot of details and changes that were last minute decisions, not the least of which has been cast turn-over. A seemingly very well developed play book is why I think Heroes is doing so well.