15X-Men: Destiny (2011)
A semi-controversial pick to start, but whichever way you cut it, X-Men: Destiny was seriously disappointing. To be fair, Destiny is at least playable, unlike some of the other list entries here, but it's the sheer wasted potential behind this one that feels like a slap in the face.
The game was an Action RPG where the player took control of a user-created mutant and could choose to join the heroic X-Men or the dastardly Brotherhood of Mutants. As the player progressed, they could level up their mutant abilities and choose how the story unfolded. To the game's credit, it featured an impressive roster of mutants and fan-favorite characters that the player could interact with.
This was all well and good when printed on the back of the case, but actually playing the thing was a different story altogether. Graphically, the game wasn't exactly a looker, with many reviews of the time noting that it looked like a PlayStation 2 title. That's not exactly impressive in the generation that switched to HD in a big way. Not only that, but the supposed player free agency boiled down to boring linear choices that barely had any impact on the story whatsoever. These things could have been excused if the gameplay was fun, but alas, it was also a shallow button masher that pitted you against the same enemies from start to finish, with little variation in between. Bad games are nothing new, but the ones that had the potential to be great and ended up bad sting that little bit more. X-Men: Destiny is one of those games.