Anytime you're forced to do stuff blatantly against the game's premise. "Company of Heroes" starts out as a decent, semi-realistic, Hollywood-WW2 RTW. Stays like that for a few missions, then suddenly you do a full blown tank rampage. I have to admit, my bias against tanks might be an issue here, but honestly, just gathering a force of tanks and plowing your way through the map is NOT good RTW.
"Assassin's Creed", where you're supposedly emulating a silent killer, invisible among the crowd, making a single, precise, deadly strike and vanishing again. Supposedly. Not only do you get secondary objectives consisting entirely of fighting large groups of guards in public, after the first few chapters the game just throws wave after wave of enemies at you.
OK, bit of a rant here.
Another thing that usually puts me off a game are characters that feel artificial. It might be that they are so underdeveloped they feel like paper cutouts, sometimes they might just be pulled straight from Uncanny Valley and strangely repulsive. Bethesda seems to be the master of that one.