This is a nice twist on a well known mechanic, well done. It is definitely the sort of game that people could play for hours with some polish. Aestheticlly the UI could do with some work and some extra sounds would make it really pop but this is extremely playable and I enjoyed it.
One small issue I had with the mechanics was that to drop the block you need to hold down, whicvh makes sense, but I couldn't hold left or right to push the blocks across, I had to just keep tapping the direction repeatedly. Its a tiny thing but I noticed it when I was trying to get blocks onto different stacks across the grid.