Regarding the whole "first time running into something I had no prior knowledge of means I am not prepared and might fail" part, all there is to say is that that's just natural.
And then you get prior knowledge and the second time you go at it, you know what to expect.
The actually difficult (and fun) games make it so the difficulty stands in how to win the fight even with all the prior knowledge you gathered. And this is where D:OS falls a bit short. Once you know what you're in for, the fight becomes straightforward: either you walk all over it, or you can't get past it, or something very close to the two ends.
A game where all surprises easy to overcome is a boring game.
A game where all surprises result in game over can be frustrating.
Now I think of games like Dark Souls. Popular games that are supposedly really difficult. I assume that in such a game, a surprise is basically game over. But it's still a popular game.
The value of a surprise is minimal when that one time occurrence is followed up by several failed attempts at surpassing the moment. But it's value is big when the surprise is the only obstacle.
Exception to this are "ironman" modes, but really, you shouldn't be going into such a mode without extensive knowledge of the game and its finer details if you expect to beat it.
So, by my potentially flawed line of logic, I think that the whole issue lies in the difficulty of the game, rather than its surprises.
In short, I think that the massive contrast between losing and winning does indeed subtract from the game. Having an easily winnable game with harsh game overs is not a good formula. Consistency is better, regardless of what area of the spectrum of difficulty the game is decided to be at.
