VICTORY! I never did figure out how to parry rockets reliably and ended up relying on a rush strategy that took advantage of my invincibility window to not die. I *barely* managed to survive the end boss fight but I did it on my second try. Gonna play diagonal tetris now...
EDIT:: Also, wow, I forgot to mention this but AnCantaloupe's message reminded me I really like how it looks when dead things lose their sword. Great effect.