After a few bosses i proceeded to play LoP:Overture on ''easy'' because everything on ''normal'' kills you in 2 hits and said enemy only goes down after hundreds of hits.
Hammering on forever makes me feel like a weak pussy.
If ''difficulty'' is pumping up the shit out of healthbar and attack numbers, you don't introduce anything except tedium which is only appreciated by the best players who dedicate their lives to the genre.
On a side note, i play co-op shooters like DRG and HD2 consistently on the highest difficulty because it is actually fun to deal with and rewards accordingly.