We played a short game of Drowning & Falling last week.
It worked fairly well, but not quite as intended. I suspect this may be about evenly due to (1) the idea being funnier to read than play and (2) that the group was not totally invested in the game.
The one notable problem was that challenge creation is a little confusing at first, and people had some trouble with that. It's also not clear whether a single character has to defeat each challenge or if every character except the challenge creator's does (we played the former).
Verdict: better parody of dungeon crawling than Munchkin, but requires more work.
Note: text version available free from the downloads section of the official page linked above.