I don't mind dying. I don't even mind dying a lot. I do mind having to replay half an hour of game because of some boulder trap coming out of nowhere and instakilling me.
It's funny, because I felt exactly the same way. You said, word for word, what I was complaining about after playing DS. I started as a soldier, got to a fork, went right, got insta-killed by a red eye knight. Back to the fork, went left, killed by a blue eye knight. I didn't know the difference, so I kept going right, and kept dying to the red eye knight until I gave up. Then I read online that I'm not supposed to fight the red eye knight yet, and he's much harder than the blue one. Also, I should re-roll as a Royal instead. "F this!" I said.
Then the weird thing happened, I got drawn back to the game. It was a feeling of, "Ugh, I hate this stupid game, but I'll be damned if I let the game beat me!" So I re-rolled, beat the level, even beat the stupid red eye knight, and kept going until the next wrong path of a fork. ;) After beating the first demon, and leveling up, the game did get easier. Surprisingly, the game also got more fun. It's a fun gained from fear for your life, like a horror game but without the scares. In other games, I see a dragon, and think "Ok, this'll be a tough fight." In DS, I see a dragon and think, "Oh, god, a dragon! AHHHHH!"
If a game is going to kill me a lot, it should either make the deaths avoidable through skill (like Ninja Gaiden Black) or it should minimize how much game I have to replay (like I Wanna Be the Guy).
This game makes the deaths avoidable through knowledge and experience. First time through a level, learning the level, took me 8 hours. I carefully crawled around each corner, carefully fought each monster, carefully died several times. But after those 8 hours, I knew the level inside and out, knew where to go, who to fight, and how. I could run through the level in 30 minutes.
But there is some skill involved too. I sat my friend down, let him try DS. I used a careful, sword and shield, approach. He went with a reckless 2-hand approach, and it worked, it worked really well. He was 1-shotting enemies that I had to duke it out with, and (with some guidance from me) ran through the first level in 3 hours to my 8. DS has a lot of freedom to make different approaches viable. Sword and shield, dual wield, 2-hand, magic, archery, etc. That said, it's also a game which benefits strongly from reading the wiki for it. There's a lot of stuff that isn't made clear, or is hard to figure out on your own. You can even do things that can seriously hurt your game, like missing a ring in the first level that increases your soul form health by 40%.