For me it's Metal Gear, I've tried the first, 2nd, 3rd and 5th game, and I just haven't been able to play them for more than a few hours, except for MGSV but even then, I didn't play that for nearly as long as I was hoping to. It's a shame because I love the style, setting, ect. But for some reason the games just don't end up keeping me wanting to come back.