Fun
Very enjoyable. The mechanic felt unique and I didn't have any issues jumping in and playing.
Aesthetics
Great. The pixel art sprites are all very well done. I was impressed there was a working lighting system. I would have liked the growth circles to have sprites as well, and a pixel art font would have been nice, but otherwise it looks great. The boss fight was especially cool.
Music
The music was alright. It could be better. The mood was right, but it felt outdated.
Sound
Great sounds. No complaints. 10/10
Mechanics
The growth circle mechanic is cool, and I like how you can choose between making a bunch of small circles, or a few big ones to change your end room rewards. The rewards didn't really feel impactful though, outside of increased max hp.
Movement felt great. It did feel a little linear though. Maybe some acceleration and deceleration? Or perhaps a dodge roll? Something to break up the movement.
I didn't like the anchored turrets. I wanted the option to kite all enemies into one big circle, and the turrets didn't let me.
Story
I liked the premise. What really did it for me though, was when you bet the game, it lets you become the son of the boss you just beat. That was a stroke of genius. I would love to see an entire game about that mechanic by itself.
Theme
This fit the death is only the beginning in two ways, the first was with growth circles, and the second was with the generational story. Both are unique and have a lot of potential.
The art and sounds also fit very well into the setting.
I do want to mention something else: The boss fight was fantastic. Those take forever to build, so I just wanted to praise you for adding one that felt satisfying.