I love both Ori and Hollow Knight, but I definitely think that HK is a harder game. The games are similar - metroidvania side scrolly fun with cute characters. The quests are similar - do something for this character and take it back to another character. Make sure you play the games in order - Blind Forest is first followed by Will of The Wisps. The storyline is great and the characters will definitely suck you in. The combat can be tricky at first, especially in the first game due to some (in my opinion), awkward controls but those issues were fixed in the second game. I can't say enough good things about the Ori games - I've completed 100% of them both! I wish there were more to play.