LOST was definitely a first in that regard, and I too am skeptical whether anyone will ever take such a risk again (even just look at how much the pilot cost!) Premium networks just don't have the necessary reach, and the broadcast networks seem to be playing it more and more safe with every year. ABC did good on this one.
It was really an event, with all the Alternate Reality Games etc. I usually TiVo shows and watch them quite a while later, in batches, but LOST is one of the very few that I eagerly awaited every episode of.
For most people though it's not a question if
, but at what point the show became bad. I only really disliked the sixth, final season. Trying not to give anything away, it was just very cheap, and the writers did everything they spent 5 years promising they wouldn't do.
But I'm not in the camp that ended up disliking the whole series for that. It was still a hell of a ride for 5+ years, and definitely made television history. Just because one doesn't like the final couple of hours doesn't mean that the many hours of great television that came before were wasted.