This fight is long from being over!
Just wanted to add some more comments on your game now that you've accepted my challenge. I really appreciate the additional insight in to making your game.
I'm going to suggest a bit of a wild idea but I definitely think you can pull it off: You could try turning the tetrominos into rooms! With how you have the platformer part setup, there's really a ton of wasted space potential. And it would really pump up the "building" aspect. All you need to do is attach a "room" behind the tetris blocks and when the gameplay starts, just plop your character into one.
I spent the entire first day working on getting the tetris part to work. The struggles of capturing the original game is completely valid. I never knew that rotating would be such an ordeal for me. And tetris god knows how many times I went back and forth adjusting my timing.
Quick comment on the style - I feel like your game could pull off using "building" textures. Like try for steel, wood, or brick, over colored blocks. I bet it would mesh really well with the other assets you already have going.
Good luck in all your future games!