The 5-piece that's a cross between a T and L is the stuff of nightmares. I had a lot of trouble with this one until I discovered there's a hold feature! Definitely a tricky take on this game design, but pretty well done and with an appealing style.
One technical problem I noticed: At power-on, you have some issues with OAM decay where you do OAM DMA about a frame before you enable rendering, so OAM has decayed by the time rendering turns back on. You could fix this by doing OAM DMA every vblank, or by simply keeping sprite rendering off at the title screen.