It's the walking and movement for me. Getting to places takes ages. Compared it most other metroidvanias, which have denser fast travel and/or more movement options, HK is lacking, the dash is marginally faster and the ultra dash is situational, basically only for dedicated spots. This isn't as much of an issue in most Soulsborne games, which HK was going for, but you don't go back to old areas as much there. Even Elden Ring's open world throws a shitton of fast travel spots and has everything you need in a small hub.
I will admit the combat didn't gel with me too much either, despite being a FromSoft fan. Not sure about that one, maybe it's the precision of movement required.
Maybe Silksong will do better with Hornet's faster movement, but I won't be buying it now.