Thank you for the feedback! :)
I think you're picking up what I was putting down with the color scheme, just from a more modern frame of reference. Since I my mindset was a "80's puzzle pastiche," I used a Sega-like color scheme: "L" orange, "J" blue, "O" yellow, "T" cyan, "I" red. I agree the "J" color could be made a bit less grey; I initially just chose colors off the default palette of the art program I loaded up.
Makes sense about soft drop. During the jam period, I just implemented a Sega-style 1G soft drop and moved on. I can definitely make some adjustments; a Nintendo-style 1/2G or 1/3G soft drop would make it a bit easier to get the piece close to the ground without forcing it to lock.
Either way, I certainly feel you on the difficulty of executing spins; the reward is so much higher with these piece shapes, but they're tough to hit under gravity lock. I wanted to explore something like Nintendo/Atari style gravity/locking behaviors, but it feels like I'm resisting the "carcinization" of puzzle games; sea creatures want to evolve to become crabs, and classic-style block games want to evolve to have Sega/TGM mechanics like lock delay. :p