MSNBC has their 
list of the top 5 video-game letdowns so far. I don't really like how they do one small page for each so I'll list them here: Atari 2600 
Pac-Man, 
Haze, 
007: Tomorrow Never Dies, Call of Duty 3, and 
Red Steel. I think I would put the Atari version of 
E.T.ahead of 
Pac-Man though and I don't really consider 
Call of Duty 3 that much of a let down and certainly not top 5. What are your biggest video-game letdowns?/