people would appreciate higher mob density simply for the sake of their being more action on the screen.
There are many places in the game where there simply aren't enough monsters, AT ALL. you can walk entire lengths of space and see NOTHING or VERY LITTLE.
when you run through 10+ screens without encountering a single monster something is definitely not right, for an action game
fix number 1: fill the empty areas with monster spawns
fix number 2: add "monster horde" option right next to monster power
-each level increases monster density
scaling could by similar to monster health in monster power:
L1 - 150% density (so instead of 10 monsters you get 15)
L10- 3500% density (so instead of 10 monsters you get 350)
that would be amazing gorefest and bloodbath :)
-each level could also increase number of elites in one pack