Really cool idea, kinda like Tetris and PvZ combined. There were some points where my pieces miraculously fit together forming a wall, and that felt pretty good. Because I didn't know what pieces were coming next I started wishing there was some way for me to plan ahead to create better strategies.
While playing level 3, I scrambled to create a huge wall and ended up with 3-4 tiles unused. I wanted to use the other pieces that kept appearing, but they didn't fit. So, a couple waves passed without me doing anything. I hoped my wall was good enough but at that point, it was a waiting game until the wall was destroyed. Unfortunately, I couldn't bounce back from that. I wish there was I way I could.
Very cool idea though, great job!