what was the biggest disappointment to you? whether it was a 'milestone' episode like 100, 200, etc. whether it was the movie, or a video game, or just an episode that sounded interesting, but upon watching it, did not meet your expectations?
the 400th episode disappointed me. not the episode itself (which would probably be around a "C" or so from me), but that it was You Kent Always Say What You Want, as opposed to 24 Minutes. 24 Minutes would have made an excellent 400th episode and IMO been probably the second best milestone episode (after Sweet Seymour Skinner for 100th episode).
I was also pretty let down with The Simpsons Game. It starts off somewhat fun in the first two levels, but I hated Marge trying to control the mob, the one where Bart and Lisa are in the video game, etc. I never finished the game, because it bored me and some of it annoyed me, like when the characters would keep repeating the voice overs (like "i hope i have time to finish my homework" from lisa in the video game level).