Let me come out of the gate with stating that I possess a lethal combination of being a completionist and a bit of a cheapskate, which results in me sometimes finding myself playing games beyond enjoyment. However, there is one game that prominently comes to mind.
Halo Wars. I got this at some point last year, due to a friend playing it and I felt like giving it a go. I went in with low expectations, just a RTS with dumbed down mechanics to make it work with a controller, with a Halo skin tacked on to give it some mass market appeal. I actually suffered through the RTS mechanics in Brütal Legend, so I knew this couldn't possibly be worse. Now the game didn't do anything wrong exactly, but despite the cutscenes which were enjoyable enough, after 3 or 4 missions I couldn't go on. Technically the game was sound enough (apart from the inexcusable framerate drops when things got too busy on screen, seriously, you're developing for a single platform, what IS your excuse), but it all just felt so run of the mill and uninspired, I couldn't bare to go on.
Another one that comes to mind, but doesn't really count because it's by now a yearly sports game, is F1 2012. As a huge fan of the sport, I spent way too much time on the 2010 and 2011 editions combined, but by the time 2012 came around, I can't make myself play it anymore. Haven't even finished one season in career, hardly any online play. I guess I'll never know if it's the fault of the game or I just played too much of this franchise in the past two years...