I tried to write an essay on this subject but it didn't sound right, so have a paragraph which will probably be clearer to grok in general.

Difficulty, despite what a few certain level designers and Korean MMO developers believe, isn't measured in "how many monsters you kill/how many crates you have to open/how big the level is". You can't assign a number to something that is, in itself, an abstract value.

Anyone that n00b described in the original post, take note: you make things difficult by adding in different situations, not the same situation over and over. Tedious is not difficult, it's just annoying. Don't believe me? Play and professionally designed level for any game and tell me how many times a certain situation is exactly repeated.