I think the reason that hidden elements in fan-made levels is so frowned upon is that there is the possibility for these to be woefully over-used. Essentially, such levels are basically troll levels, with the intention to annoy and mislead the player. Conversely, a level which uses a single hidden trap can hardly be considered a troll level; rather, it is one which requires the player to remember where the trap is each time they play the level. This has been considered by some as "fake difficulty", a term which I find problematic because the difficulty is not fake; if a player genuinely has trouble remembering where the trap is, then it is an added layer of difficulty which I believe to be acceptable - again, iff used sparingly rather than excessively.
No, that is not why. Even a single one is annoying as hell when you have a solution that should work, only to run into a trap that there was no way to know was there and have to go back to square one. It doesn't add any challenge to the level. All it does is say "haha fuck you, you can't do it that way" to the player when they're taking an approach that, were it not for a trap that there is
no reason to expect is there, would work. Except for annoying the player, a hidden trap never achieves anything that a visible trap cannot. If you don't want the player to take a specific path, put a
visible obstacle on it, or carefully set up the skillset so that the path doesn't work out skill-wise.
Or to put it another way: It's the Lemmings level equivalent of a riddle where every time someone comes up with an answer that fits but isn't the one you wanted, you just say "nah that's not allowed, find another answer" over and over until they get the exact idea you had in mind, rather than crafting the riddle better so that the other answers don't fit.
The difference between a single and multiple is that, while the former is likely to just get the one level written off as bad, a pack doing it over and over is likely to get
the whole pack written off as bad.
Show Posts
(And I guess there's also Paintball and Lomax, but I'm not going to push so hard on those ones. 
)