I bet a lot of you are already brandishing your pitchforks, and duly so - Saints Row The Third honestly isn't that bad. Hell, considering most of the games it shares this list with, it's considered a damn masterpiece, but from my perspective - yeah, it was a disappointment, all right.
Let's start with the story. Previously having pretty much conquered Stilwater, your character - the head of the eponymous Third Street Saints - is robbing a bank with your most trusted crew members when your plan goes a little awry and you and your crewmates end up locked up, upon which you meet the bad guys, the Syndicate. They take you aboard their private jet and discuss business with you, you decline because they're assholes, and they unceremoniously gun down one of the series' most long-standing protagonists off-screen.
But it only gets better from there. You know how in order to progress and level up your character in the first couple Saints Row games, you had to experiment and try out some of the side missions? This game just says 'fuck it' and throws them directly into the main game for no reason other than to pad out the story's length. That's not the only substantial change made to the game's story, either - you can no longer tackle each rival faction separately with their own sets of missions, as they are all one big superpower, so the missions play out in a boring, linear, and uninspired fashion, made even better by the eventual involvement of the cyber military. The game essentially turns from a thug drama to a ridiculous sci-fi/action comedy for no reason, and despite some really neat concepts like the level where you fight the Deckers inside cyberspace, most of it feels jumbled and incoherent with itself. It jumps from one idea to the next, throws the wackiness switch on overload, and completely loses the magic that Saints Row 2 had, because while the second outing had its spurts of comedy, it was mostly backed up by a serious, somewhat-believable plot. With The Third, however, silly shit is happening and in your face 24/7, and it turns old hat very fast.
If I upset you for lashing out at this game, well, apologies, but you have to remember that I highly anticipated it, too. The fact that the payoff was quite underwhelming gives it good enough criteria for me to include it on this list. Remember what I said earlier - a game doesn't have to be bad for it to be a letdown.