How hard is a level?

When playing the new 5x5 levels today I noticed that it's really quite simple to find out whether a level is fun or not: If you count the armor+amulets in a level and compare that to the number of monsters, then typically

• Levels where monsters outnumber a+a by 2:1 are tough and not fun; typically all you can do is find a stairway down before they find you.
• Levels where monsters and a+a are about equal are fun.
• Levels where a+a outnumber monsters by 2:1 are too easy.

Strangely enough, the pure numbers don't play such a big role. If it's 10 monsters and 5 pieces of armor or 20 monsters vs. 10 pieces of armor doesn't matter.

Maybe I should take this into account when selecting levels while parsing the web pages...