Lost. I watched it when it originally aired, and it was rather unexpected. I went in thinking it was going to be a drama along the lines of Survivor. Then there were these loud sounds similar to dinosaurs, trees bending and swaying as though a T-Rex was heading for the beach, just a whole lot of odd shit.
If I only knew that the things that were so captivating would be dropped from the story as though they were an afterthought.