Congrats on such a well built game for being so new, I was no where near as good as this when I first started. I also appreciate the Metroid inspiration :)

For some pointers, I think adding a sound track helps make games feel more atmospheric. For me, I had 0 time when considering music, so I just used Freesound.org for basic sound effects and background tracks, you can search for a lot on there. Adding audio to Unity is incredibly quick and easy too, you could do it in 10 minutes tbh.

Do you happen to be using forces for your player's movement? The player feels a bit floaty and quite slow in general. You can remedy this by having the RigidBody2D of your player gravityScale change depending on if your upwards velocity is positive or negative. This makes jumps feel way better to use in my opinion. And also just increase the horizontal move speed a bit.

For one last thing, I think it would be better if the mini platforms were semi solid, so you could jump upwards through them, but won't fall down. For my game, I did this easily by making a box (with rigidbody (set to kinematic) and box collider), and putting a "Platform Effector 2D" onto it. Select the "use one way" box, and it should work!

Overall, great job!