A different aspect to traps: Rewarding the player if he manages to detect and not activate them.
It's incredibly fun to lure enemies into traps you have not triggered!
I do this whenever I can. In Oblivion and Skyrim, where traps are generally very weak, I would always take my time and lure enemies into them, knowing it would be much easier to just smash their head with my axe. It adds a certain aspect of slyness and Schadenfreude.
I totally agree, those kind of traps feel really rewarding ^^
I think even if there is an infinite number of possible traps variations, it may possible to put them into some categories, like : (All of the following is personnal thoughts, they may be totally wrong
: I think this is the first kind of trap that people think of when they hear the word 'trap', They're mostly not or partially visible, and will (for example) kill the player, and the next time the player get next to it, he'll have learned the lesson and avoid it...But sometimes the trap could be designed in a way that the player can escape it once it have been triggered (Wich feel much more rewarding and make you feel like you're good :D)
: When you cleary expose the trap to the player (it's more an "obstacle" than a "trap" at this point") and the player immediatly sees it on the screen, he begin to think how to avoid it, so the surprise part is gone (But you could change the trap at the last second wich is a trap in trap !).
That could be handful for creating hard situations without them being frustating (Like in meatboy : Every single obstacle is clear, and never 'trick' you), otherwise, the player may find it unfair
The visual aspect does matter a lot, with bad art the trap can be totally mixed with the backgroud (Or that can be the purpose), or just look at Luigi's mansion fake doors for example (I don't know, just came trough my mind), they used the exactly same models, texture, as the real doors, and even their locations seems legit, no way you can tell if they're fake or not the first time...But it's alway funny
But I don't like put things in categories, and in the end the right trap is always the one that does not feel unfair
And I realize that the point of the topic was to give example, sorry