I think games need to be in the middle, challenging, but not too much. If a game is too hard and I keep dying, I'll get bored with it or frustrated (depends on the game and how I die) and just quit. If it's too easy, I won't feel any satisfaction winning. It has to be in the middle.
Most games today have difficulty levels to satisfy everyone, so that's great. I usually play the games on Normal (usually the diff. setting the developers intended for it to be played).
I really won't like spending ages on a game just to pass one point or level, wasting many hours. I'd rather pass it with a decent challenge in a relatively short time. I got other games to play, and a life to live. Can't spend 10 hours trying to beat one stupid boss or something.