For me, the original Hollow Knight wasn't exceptionally innovative or original, but did set an extremely high bar for polish and refinement over similar indie games. I've played a lot of metroid-style games and Hollow Knight has super tight movement, and expansive and thoughtfully interconnected map, simple but addictive combat, great art and design, memorable music, etc. Plenty of other games have some or most of those things, Hollow Knight just executes them at such a consistent level of craftsmanship that it stands out.