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.
Gabriel Knight 3. Worse in every way to the previous two. Horrendous 3d engine, bullshit (impossible) puzzles and terrible voice acting.