I've been playing this on the highest difficulty (because I'm a stupid moron) right of the bat and there are certainly pros and cons to this game. I just beat the fourth boss, which took me about two hours of retries. There's a lot of things to learn about each encounter, and most attempts gave me lots of new ideas, so... off to a good start. However, there are certain problems that become amazingly frustrating quickly.
Unlike, say, Super Meat Boy, it rarely felt like my deaths were fair and completely my own fault. Instead, the boss randomly decided to forego certain things in his pattern for no apparent reason, the wall grab falling to register because it requires a pretty counter-intuitive input and the worst part of all... There's a hugely punishing cooldown on the only defensive measure you have - the cancel dodge. This meant I had to play around the boss and stay passive for several seconds at a time because any offensive move is quickly punished if you cannot i-frame out of it. This becomes a huge problem because the boss pretty much requires you to stay on him with permanent aggression in order to not get overwhelmed by adds etc. Literally a single fuck-up (due to some quirk of the controls) would completely ruin your momentum and destroy any chance of further pressure on the boss itself. In the end, I managed to do a flawless attempt, but it honestly didn't feel very satisfying at all.
Such a shame, because a game like this is something I've long dreamed about. It kind of feels like the devs didn't really design their game around being able to perfectly play through the hardest difficulty, which you can tell that games like DMC (an apt comparison when it comes to difficulty) certainly were. Still, I'll keep playing it because it is so challenging. Definitely worth the sale price.