Jericho, a show that pretty much no one watched, and with good reason.
Jericho had a terrific premise and tons of potential -- it was about the reaction of citizens of a small town in Kansas to a nuclear attack on America. The idea was to make a small, personal drama (love, loss, and conflict amongst the residents of a small town) set against a huge, epic struggle (the aftermath of a nuclear holocaust), blended with the teased-out enigmas and mythology of a show like Lost (the town of Jericho is cut off from any communications with the outside world, and we don't know who launched the attack or why, whether or not the U.S. fought back or was occupied, or even whether or not other nearby towns and cities survived, leaving tons of mysteries to be solved).
Unfortunately, the show stunk. The actors were uniformly bland and uninteresting, from uncharismatic lead Skeet Ulrich on down; the personal dramas were boring; the dialogue was a blend of dull, predictable and overblown; the characters aren't particularly interesting; and the mysteries are teased out way too slowly. For me, it ended up being a wash; I quit watching a bit more than halfway through season 1. Maybe it got better after that; I don't know. I do know that angry fans noisily petitioned the network until they gave in and produced a second (half-)season, but its ratings were even worse than the first and it, too, was canceled. I never saw a minute of the show after episode 14; by then it had so thoroughly squandered what I thought was tons of potenial that I gave up. I can scarcely remember a show that had so much potential and delivered on it so little.
How about you? What's a movie, TV series, book, comic, or other entertainment vector that you thought had tons of potential possibilities and more or less squandered it all? What are some of your biggest entertainment let-downs? (First person to mention Star Wars gets an ax in the neck.)