To vent out from the exams the whole group finished not long ago, I'm preparing a simple D&D3.5 game. A mindless dungeon crawler with lots of enemies, loot and the usual stuff with just enough story and background to keep things together, as in games like crawl, nethack and such.
The thing is, I like to drop surprises, traps, twists, puzzles/riddles and unexpected events from time to time to make the world they are playing in as unpredictable as possible (They can do whatever they want, but so do NPCs). The players know this and like it, but they told me not to put "too much" since we all want to chill out and not think too hard.
I already intended to keep the puzzles and riddles to a bare minimum (Maybe one or two ridiculously easy ones), but I'm worried they will find any slight event twist, trap or quest as too much. It's mainly about having fun not even worrying about the characters, so I don't want to overdo it.
I tend to improvise everything except the basic story outline and some fixed stuff so I don't have any problems dropping new and unexpected things in the game if I see they are bored or removing them if they are not having fun, but I'm afraid of giving them an event that will kill the mood completely.
My question is, when are riddles, event twists and "general thinking stuff" too much? Specifically on a dungeon crawler as the one I described.