As a big metroidvania fan, I'd like to introduce a few of my favorites that go beyond the obvious choices like Hollow Knight and Ori (which of course are excellent). All of these are straightforward and while difficult, they don't focus on confusing menus or min/maxing statistics.

Astalon: Tears of the Earth: If you play one game on this list, play this one. You play as 3 characters, each with their own abilities, and can switch at certain save points. You die a lot and have to start over from the entrance every time, but the game gives you plenty of shortcuts and upgrades that you can quickly go back to where you were. The map is great to explore and there's a lot of content to keep you busy like a boss rush and new game+ modes with different characters.

Momodora: Reverie Under the Moonlight is a short but sweet experience. It's difficult but not unfair enough that you want to stop playing, the world map is well designed, and the pixel art is great.

Rabi-Ribi: This game looks like it was made for a very specific (horny) crowd, but there's a surprising amount of depth to the world and the bullet hell boss girls that inhabit it. It's an interesting mix of bullet hell and platformer that somehow makes up for the nonsensical story.