A lot of strategy RPGs...
It isn't that they are that terribly difficult, it is that I do not often have the patience to slog through them and end up rushing every aspect in order to progress. After a while, that ends up biting me in the ass.
I made it through Final Fantasy Tactics, though...but that didn't seem too difficult. I've tried a few others (like Hoshigami) before and had a rough time with them.
I would also say that I am no good at 2D fighters.
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I enjoy playing them, but I have never been good. The problem is that, when they were REALLY popular, I never enjoyed them and therefore never really learned to handle them well. Now, when someone I know wishes to play a 2D fighter, that suggests that they are decent to good at them...and while I DO want to play, I really suck at them and end up having little fun.