The satisfaction of feeling your set of abilities and options for gameplay increase and grant the ability to overcome previous obstacles is the main thing I expect and want from a Metroidvania. I felt like this was Hollow Knight's biggest weak point. It just didn't feel like you gained new abilities at as steady a pace or as though they opened up enough of the world each time compared to other games in the genre, including Ori and the Blind Forest. I think Super Metroid still has the best progression among Metroidvanias, but it's possible that's colored by my having first played it at a young age.
That being said, they are still very good games; excellent atmosphere, artwork and presentation, some genuinely haunting, creepy, and awe-inspiring areas. But I think Hollow Knight is a tier above them.
Personally I find combat to be one of the less important aspects of Metroidvanias. I prefer the main source of difficulty coming from platforming around environmental hazards.
I felt like exploration in Hollow Knight was a bit too broad, and lead to too much unnecessary backtracking. Backtracking is a balance. It's a staple of Metroidvanias, but if the backtracking search space is large enough and places aren't distinctive enough then the search for a previously insurmountable obstacle can start feeling like looking for a needle in a haystack. That was my experience in Hollow Knight, and something I felt like the first Ori game did better.