It was really fun and had some puzzle elements in the beginning, but at a certain point in the mid-game that falls by the way side. There were some things that felt active just for the sake of having interaction, like the charge stuff and the fact that upgrade charging could never be kept between Double Compressions, but they were never too awful. Decently fun overall.
Also, why couldn't there have been one last upgrade for an even 4x4? :(