Haven't been able to get into either one really. Hollow Knight feels really aimless, at least early on. I have no idea where I'm supposed to go or what I'm after. I'm sure it gets a lot better but haven't put more than 2-3 hours into it. Unless I've missed something the game really doesn't give you any objectives, and even after I invested in a map I barely feel like it helps.
Dead Cells feels less aimless but kinda brutal difficulty-wise, have done about 10-15 runs making it not very far each time, just feels like a grind to unlock some stuff to make things easier. It feels a little bit like Enter The Gungeon did early on though and I got super hooked by that when I invested more time and got past the early grind, so I have faith Dead Cells can be the same.
So I would say my first impression is that neither one is making a huge first impression on me.