It was really hard for the first few hours, but after that, it just became easy. I could kill anything by the time I reached the second region, so the nemesis system really did nothing for me from then on. If by chance a captain would kill me, I would just go find them and kill them straight away to get revenge.
It's a shame, I was forced to finish the game because I had no reason to play around with the nemesis system. The upgrades I picked were apparently too powerful and the runes I got were also apparently too powerful? for instance, I got a rune early on that gave me health for killing an enemy.
I know people will say to not use that rune or don't unlock the double finisher skill, but that's a fault of the game if me playing the way I wanted to ruined any sense of the difficulty. At that point I'm deliberating handicapping myself and if I'm having to come up with ways to make the game interesting myself, then something has gone wrong there. I want to play the game again so that I can go back to before I upgraded myself but the tedious and terrible campaign missions (aka 19 tutorial missions and then the final boss mission) just remove any desire for me to play.