I've played a few rounds on normal difficulty. Very doable, except for the final boss who has killed all of us every single time. Still haven't defeated him. He takes a metric-shitton of damage, like holy cow, I don't remember the Patriarch from KF1 taking this much damage (but of course he probably did and people just had the time to get really good at taking him down). This is playing with people who are level 3-5's, so we're not exactly total newbs either.
Also - because I'm pedantic - "the patriarch" is the name specific only to the final boss on KF1. The name of the first new final boss in KF2 (there will be more than one) is
Hans Volter.