What flaws do you look in a game to consider it bad?

[flagship]

Poorly designed difficulty curves, lots of games turn out terrible simply because they become way to difficult or fail to pose a challenge, it's very hard to get the right mix that makes a game challenging enough that the inevitable repetition is enjoyable while not being so difficult that you waste hours replaying the same 5 minute section again and again which in my case typically marks the point where I simply stop playing.