Most of good level makers (all?) can make a decent eyecandy.

By the way, I'll just add one more thing -

Levels with bad flow

I dislike levels where everything is so tight and wherever you go with your full speed and momentum, you just hit or bump into the wall (some spots on Diamondus Warzone). It's just bad to always watch out not to hit a wall and lose momentum and speed. JJ2 is pretty much all about running around and shooting - that's what most of players actually do. You, indeed, need to stop at some times and not just rush. But with good strategy and good ammo mixing it's all about fast running and spamming ammo. I like levels that are more open, but not so much because you can get air hit more often like in JE.