For example, Angel of Pacifism. I've gotten to level 12 or 13 on that. I understand that they're supposed to be a challenge mode or whatever, but some of them aren't even possible. Like there is no way you can beat AoPc or AoH on anything higher than HMP without save scumming or breaking the game in some fashion. I like a good challenge but I don't like trying to turn a concrete building into gravel with my forehead.
A lot of this depends on what you're looking for in a challenge. Sometimes the challenge is to wait for the right game to give you a break (more often, wait for a game to not give you a literally-unwinnable situation) and, until then, play as best as you can as a matter of practice. Maybe you think the difficulty stepladder is too steep? I actually went directly from HNTR to UV without once touching HMP, and didn't play ITYTD until beating HNTR anyway (which only took a few weeks' worth of slightly-less-than-casual time). I do understand your point, especially for challenges like Angel of Pacifism, where a large part of the game depends on you doing basic actions and the game restricting those very actions. That's why I removed the Pacifism Platinum and Diamond badges (and reduced the difficulty for Bronze-Gold): trying to make a reward for something as unbalanced as that mode was ridiculous, so I went in the direction of "easy with tight conditions". In general, I'd like to make it so that all of the badges are in the vicinity of feasible, given decent rolls in generation and tactical and strategic know-how. We're probably not there quite yet, but I imagine that most of the hardcore players have noticed that the Diamond series is easier.
Regarding the balance of specific challenges on specific difficulties, it's actually a developer decision to affect the game as little as possible when introducing new challenges. For instance, other than Hell's Area, there are almost no instances where a specific challenge affects monster or item placement in special levels. It's not like we remove all ranged weapons in Angel of Berserk or all powerups in Angel of Purity, simply because the player has no use for them: the challenges are explicitly intended to restrict the player, sometimes to the point of being unfair. So it's probably not even a matter of subjectivity, this game is just downright mean to you with certain settings. As long as we're not asking the player to do these things most of the time, I think that's okay, especially here in the roguelike community.
In short, if you're playing with a challenge and difficulty combination that you find too unenjoyable, I would recommend not to play it. There are tons of ways to play this game (which will increase dramatically next version) but it's up to you to find what ways you enjoy.
You can make another ultimate secret or x of them. And DS won't be alone anymore.
For all you guys know, there ARE some new ultimate secrets, and nobody's found them yet. I'm not spoiling anything though...