Cool concept!
Couple of feedback:
- I was lazy and didn't read the instructions at first since they looked long. Went back and read them after a couple games and they were good - but you might be able to make things a bit more intuitive in-game
- Even just putting the word "Power-ups" or something over the bar of available special items
- Having tooltips or a text bubble when selecting a power-up would be good even if it is a short description
- It seems like the power-ups came in pretty fast. It could be a bit more strategic if you get less of them, but with more it is kind of more fun ha