If curses are going to add any really interesting flavor to the game, they have to be (1) not deadly and (2) very hard to discover.
If the curse is deadly then the item will never be used, so deadly curses are not very interesting from a gameplay perspective. But if the curse is hard to discover, as you suggest, then the player isn't making an informed choice (or any choice at all), and the curse is similarly uninteresting.
One way to tempt players might be to make curse activation very rare. For example, consider an aggravation curse which has a 1 in 1000 chance of aggravating every creature on the level. The curse must be significant enough that its activation is a non-trivial event, but rare enough that the player isn't annoyed.
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