Personally, I find if a game is too frustrating, I don't enjoy it.
Same goes for if a game has no challenge in it. It's dull.
But there's quite a broad range in the middle that I do enjoy.
Some of the Sonic games come to mind. I love them, always have.
Some levels and bosses are a complete breeze, done first time, A rated the level or whatever, too many in a row and I get bored.
Others are so infuriating that I have to take a breather and play something else.
Others are just right, provide enough challenge that it's fun, even if I fail a couple of times, but not so much I have to keep doing the same but over and over again.
ED oddly falls across the entire spectrum. Combat, I find almost completely lacking in challenge, I have to force the difficulty to get any real sense of victory from a battle. But then finding information without outside tools is an exercise in frustration, and I simply can't be bothered.
But, it's still one of my favourite games ever. Lol
Joining in the OT discussion, I think that anyone who says video games make you violent is completely wrong. Being prone to violence is a mindset, that you're probably born with (I don't know). You'll be swayed by anything violent; TV, movies, friends, and games.
I'm not at all a violent person (pretty soft actually, I don't even like hurting insects, except spiders! Evil!), but I've played violent games for as long as they've been out.
Duke Nukem and GTA comes to mind, but many others, including Soldier of Fortune, or Die by the Sword, and really old games I don't even remember, and I'm harmless. Lol