For me: Ni no Kuni - Don't get me wrong, I love the characters and the story, but the battle system kills it for me. I pretty much have to watch the rest of the story on youtube >_< All in all, I just lost interest.
Assassin's Creed 3 - I was super excited about this that I even bought this digitally on the first hour it came out. It started out great, but as it progressed I started to lose interest cause I just found Connor to be plain boring and unlikable, and the framerate in the big cities is horrible. This has to be my least favorite AC game.
I couldn't finish these games cause I lost the motivation to.
1. Bioshock: Critics raved about it, and I was left wondering if we played the same game. 2. FFXIII: I never would have imagined that SE could produce something so stale. 3. Resident Evil 5: The reason I haven't touched 6, and will probably never go back to RE.
RE6: Leon's story was ok, but the other ones were horrible. I'll never buy another RE game because of this.
Prototype 2: This one is a little strange. I think the combat is an improvement, but at the same time it's a step backwards. I missed being able to hit triangle and have spikes come out of the ground, but I like being able to use two powers at once. The story though... bleh. It was awful. The main character swore all the time, and I think it was in poor taste. Anyone who has played it before, will probably agree that that's not even the worse part of the story.
Fable 2 &3: I loved the first Fable game so much, that I actually bought a 360 when Fable 2 was released. My god it was awful. You can't die, ever. What's the point of even trying then? The armor didn't affect your stats, why not just run around in your underwear then? *SPOILERS* The last boss isn't even a boss. You can sit there and listen to him talk, then your team mate kills him for you. Or you can use the music box. Then when Fable 3 came out, I had to get it. Again, no bosses. No challenge since you still can't die, and you have infinite magic (second one had infinite magic too I believe). But at least the last boss you got to fight. Awful games and I'm done with the series.
Do systems count? If so, then the Vita. I've had it over a year, and I only have one game for it. Hopefully they release something good soon.
Drakengard 3 is announced! I won't remove this until I the game is released, to spread the word!