You know games like Rogue Legacy or One-Way Heroics or other (usually procedurally-generated) titles where you lose but make progress to assist you in making it to "the end"? Okay, this is that, but incredibly abstract and with no explanations given.
A lot of people recommend going into this blind. I'm gonna break this down into two tiers of review: one that's incredibly minimalist and gives away as little as possible, and one that'll be more detailed for the curious who give no heed about spoilers.
THE BRIEF REVIEW: Game only uses a few keys total. Plant seeds which grow in different ways/have seperate effects based on their color (or shape, if you have colorblind mode on). Your enjoyment will greatly hinge upon how much you want to experiment with this process until you figure basics out. Hint: grow upwards, grow outwards, and remember you can delete blocks beside/below you.
THE SPOILING REVIEW: Seriously, stop reading probably.
The game gets a little repetitive as you try to 'grow' Green blocks because they have block seeds in them. Your journeys into the resetting world(s - plural, you need to explore to find new ones) will be based on reaching a black speck in the void to get a key, so you can get inside the structure you've grown, grab the seeds, and use the gate at the bottom to make it 'home' with your haul. Use those to grow out the permanent structure, and find new places/some worldbuilding text.
Do this for a while, blindly seeking out the next area with whatever construction you create. That's the game, and as far as I can tell, it does not change. I cheated and looked around to see if I had anything new coming and went "I think I'm good here" a few worlds in. Not bad, but decide for yourself if this seems like your bag, spoiler-haver.