6. Broken Lock-Ons
In a lot of games, a lock on system is basically vital. It both lets the game know what enemy you are specifically trying to attack - so you don't end up just auto-aiming into whatever is closest - and also allows you to properly focus on one foe without getting sick from the camera roaming around wherever it wants.
It's a great system - right up until it's not. If you get a game where the lock on randomly swaps between enemies, or god forbid randomly deselects, you can feel personally victimised. It's frustrating to feel as though you as fighting against the game while trying to play it, and this feeling is never more potent than when you can't even hit the thing you're trying to.
Many games have developed ways around this by allowing you to customise how lock-on works in your game settings. But far more are sort of happy to leave you to it, and while it's not a cardinal sin for a game, it's definitely annoying enough to make whatever sense of immersion you had gently evaporate.