Some danger is good, but there's an obvious line between annoying and challenge.
Lets talk about nanawa mines. When i went through the first few times it was mites and chigoes and terrible skeletons and the gnat/bardi rooms. If it popped it certain rooms you werent finishing it(at least without sac pulls rushes etc). They then moved some of this stuff and reduced some of the aggro you had a mite or two to worry about and things generally didn't spawn in a horde of aggressive stuff. Then they removed the aggressive rooms and have like one aggressive monster. I basically did it on auto pilot last run through. It wasnt as fun for taking the same sorta time.

I recall when level 50s popped on the road near level 1 players too- no thats not fun. Level 10 or something that maybe doesn't instant kill is nice- i guess what im saying is:

Danger not Punishment