Why It Was 'Too Big'
With the incredible success of Lost came a bunch of network executives scrambling around to find 'the next Lost'. A number of shows crashed and burned harder than Oceanic Flight 815 , but none were quite as hyped as FlashForward.
This one had the benefit of actually airing on ABC, the same network as Lost, so it wasn't just billed as being the next Lost but also its direct replacement. Based on Robert Sawyer's book of the same name, it had well-established names behind-the-scenes, with David S. Goyer (The Dark Knight Trilogy) and Brannon Braga (Star Trek: The Next Generation) producing, while ABC gave it a massive promotional push. It couldn't have asked for a much better start either, with a great pilot watched by around 12.5m people.
Why It Failed Anyway
Unfortunately, those viewing figures were completely unsustainable, and had pretty much halved by the mid-season point. It quickly became apparent that the series had very little direction, nor the ability to sustain even one 22-episode run, let alone multiple. Showrunner Marc Guggenheim was replaced after just a month on air, and replacement David Goyer made for a complete tonal shift before he too departed just a few months later. The show's mysteries span out of control until it was just a complete mess, and ABC promptly cancelled it after one season.