You want us to disagree more?!? Is that even possible??

Let's see... A level should have losta dead-ends for strategy, no flow at all, it doesn't even need organized eye-candy, random ammo placement (who cares?!?), and it must (and I mean must) be ripped off from an official Epic level.

But seriously, you can't really avoid these fundamentals. I feel that all a level really needs is the basics (as listed previously by everyone else), especially originality. I think that's the best part about levels, and without it we'd probably get bored of seeing the same old thing. I kinda see it like this (tentative):

1. Originality
2. Layout
3. Eye-candy
4. Ammo Placement

That's all I have to say for now (to be honest, I kinda had to rush this). And so this is my general opinion on how a level should be made.