A stories' difficulty level; how and what?

Hiya, everyone.
I was working on my level up until I started writing this, and while making it I started thinking about the difficulty levels.
Since I always made solely environmental levels, that wasn't a problem, but now that I've added enemies I've started to wonder about this.
As far as I know, there are no real 'guidelines' for the difficulties: the creator just calls it 'hard', 'lunatic' or 'easy'.
But how should a creator judge that? Should he judge it after the general level, or after the difficulty of the most difficult obstacle?

I myself would choose the last option; there are probably many others as well, though.
That's why I thought to post this here, to gather some opinions.

So, what do you think? How do you judge the difficulty of your own stories?

I think the settled upon "rule" was to judge based on the single most difficult obstacle. And it is highly advised that you overestimate the difficulty since you've probably been testing your challenges many times and they seem easier to you than they would to the average player.

I judged the difficulty of my own levels by comparing them to Nifflas's (which may not have been a great idea, since he tends to downplay difficulty, but I also overshoot it, so things even out in the end ).

I think the settled upon "rule" was to judge based on the single most difficult obstacle.

If there are multiple endings and/or secret areas in the level, I believe the consensus was to only consider obstacles on the way to reach the "normal" ending.

If there are multiple endings and/or secret areas in the level, I believe the consensus was to only consider obstacles on the way to reach the "normal" ending.

This is the way I see it as well. If the whole level is very easy but there's a secret room with a lunatic puzzle to reach an extra item, it would make no sense to say that it is a lunatic level.