This post came to mind after I played the new MW3 campaign. For me personally it has to be Wolfenstein: Youngblood. That game was a complete disappointment compared to the rest of the new Wolfenstein games. The only reason I ended up finishing the game was because my friend and I were playing it together and decided to tough it out and see the end of the story. Gears of War: Judgement is another dishonorable mention. A game that I did not like at all, but continued to finish it solely because I had played every other game in the series so far.
Personally, I loved that game and played all the way through to the final difficulty