That's why you can't throw keys through a portcullis.
my shortest game of dm was thus: level 1 pick up gold key throw through portcullis.
second shortest game: throw iron key trough portcullis to kill screamer level 1
(you can definitely throw keys through )
apart from dead ends
sometimes real show stoppers(teleporters/puzzles with tiny switches/monster lure not obvious) are not unforgivingly bad.
You can accept that if you eventually find a solution to it. It is not nice but as said ok if you can get around it soon enough.
I would tend to say that CSB is too difficult for the standard player. You have no real starting point for instance. I bet a lot of people get starvation problems or simply get killed soon.(ok if you like to reincarnate your characters, you are probably the fault here

CSB is for advanced players I would say. It did not have the same following than dm after all, no?)
The original DM Java dungeon was really impossibly difficult.(food drain bug I guess) But that is another topic.
anyway you need to get directions (map in game or knowledge by playing/obvious routes or map paper and pen)
I have only really once seen a too hard to figure out puzzle that had been crucial to beat the game.
Well, sometimes you feel delivered to the whim of the dungeon. Makes you really feel not good. Probably conflux tends to make you feel weak?
Trantor is right: DM is linear in the first few levels, they are rather boring. Make the test and backtrack to the starting point if you where on level 13 already.. not much happens there.(was fun on one occasion there had been a stone heap monster that I blasted away with a mon ful ir- it instantly incinerated. What fun to beat it in 0.3 s.)
If you do not need to get there(the beginning) again, this is actually ok.
ok,I wish you good dungeon building!!