Thanks for your answer, Innerscope.
One of the alarming design flaws to this sort of game is that a player could design their dungeon to be impossible for other players to pass.
Making the creator test it himself would probably also lead to people playing his own dungeon 500 times until he completes it once.
I already have some ideas to prevent this and currently favor an idea from the above mentioned thread: you will only get the reward for killing other people, when someone has finished your dungeon. Another option would be "test runs". You have to pay some amount of gold to open your dungeon for 10 test runs, of which at least 1 person has to get through it.
I have to wonder though, what kind of answer you're expecting from the question you ask, or even what you'll do with that information.
It looks like my initial post was too much about the general idea instead of what kind of feedback I was looking for.
There are 2 possible solutions to advancing in the game: rating (which can also decrease) and a simple experience/leveing system.
A rating system would want you to always give your best and reward you for clever dungeon design, which is not used too much. Unique dungeon designs are obviously harder than common ones. However, if you fail at the dungeon design oder have a bad day at playing dungeons yourself, you could lose a lot of rating, which would not be fun and probably be more appealing to a hardcore crowd. Adding a ladder, world records and making a dungeon last only x days could easily add a lot of reasons to keep playing it, if the gameplay itself is fun.
Using an exp/leveling system would make this a grind fest and kinda similar to those browser "strategy" games, only with an active platforming part added. People would reach the top after some time and have no reason to continue playing. They could try to make the hardest dungeon possible, but I doubt it would be enough to keep playing.
A rating system seems obviously like the better choice, but I fear that not many people want to play a platformer that will punish your mistakes. At first it looks like the exact opposites: people playing super mario and people playing counterstrike/starcraft. Looking at the success that super meat boy had, while still being kinda tough for the average gamer, makes me a little uncertain.
Would adding "punishments" for dying make this only appeal to a (too) small crowd, even it's reason is to improve the gameplay experience?