DCSS has a number of problems, but most of them come back around to hypocrisy on the part of the dev team in one way or another. One of the simplest examples is how they parade the game as allowing the player to beat it with no prior knowledge of the game, in contrast to NetHack, where you can gain a really distinct advantage by memorizing spoiler post like Bible verses. But this just plain isn't true. DCSS is just as bad about this as NetHack is, perhaps worse. It just relies on a different kind of spoilers from NetHack.
NetHack is a highly strategic roguelike. It's less about the way individual fights play out (heck, it's barely even about the fights at all) and more about the goals you set and your plan for achieving them. The strategic depth in NetHack is incredible -- if you want something to happen, you can make it happen if you know what you're doing. When it comes to major decisions in NetHack, there really isn't any wrong answer. If you die in NetHack, it's probably because you made a short-term tactical error: maybe you forgot that minotaurs didn't respect Elbereth, or that a wand that makes the floor engravings vanish could be turn invisible as well as teleportation.
DCSS, on the other hand, is a high tactical roguelike. It's absolutely about the way individual fights play out. It's about resource management, preparation for battle, and taking advantage of what resources you have in the heat of battle. It's quite deep in this regard. This means that the game is more like a series of self-contained encounters with bands of monsters which you either survive or don't, and the preparation between those battles. The rest of the game literally plays itself on autopilot. If you die in DCSS, it's either because you made a short-term tactical error (probably something along the lines of forgetting that you can't run away from jackals, or that it's a BAD IDEA to engage those orcs with their priest in line-of-sight) OR because of some long-term strategic error, probably something like training the wrong combination of skills.
Now, in both games, the tactical errors are pretty easy to pick up on. The difference is that in NetHack, there's a lot of esoteric information to learn on the wiki that can improve your play -- there are some fantastic techniques that are completely inaccessible to you if you don't know the ins and outs of how a specific item works. DCSS looks at that and says, "That's bullshit; Players shouldn't have to read the wiki to figure out the best way to play," without realizing that it does the exact same thing with overall strategy! How is the player supposed to know what specific combinations of skills will lead the way to victory without spending hours reading up on strategy or with even more hours of trial and error?
Another problem with DCSS is that it assumes all players will take every advantage they can get when playing the game, even if it means doing extremely boring things. They removed Nemelex Xobeh's sacrifice mechanic because it meant that players could gain an advantage from playing "dungeon janitor" and sacrificing every piece of junk equipment they came across. According to NetHack's philosophy, such strategies are their own punishment. According to DCSS's philosophy, simply having that strategy possible in the game forces the player down that path.
Another example is the way DCSS discourages grinding. They have a food mechanic, yes, but they also have an OoD clock: if you stick around too long on a floor, stronger monsters will start to show up, forcing you onward. Some players, including myself, would use this mechanic to tempt fate -- wait around on the floor for the strong monsters to start spawning, and then face those monsters down to reap EXP rewards. This was a fun and exciting way to play the game.
Then the developers said they intended to crack down on this strategy by removing the EXP rewards for monsters spawned in this way.
I realized then just how short a leash DCSS kept is players on.
