Extremely cool idea. Love the snappy feel, the visuals, juice elements all really drive the point home.
It's very difficult, even accounting for the fact that one may be used to the polar opposite game setting (of a more offensive style). I like that, personally.
The overall design felt nice and uncluttered. Kind of reminded me of Smash Hit (a mobile game).
I will say that the tutorial confused me a little in the beginning. Could be attributed to the unusual design, though (as compared to offense). Maybe it's just me, though.
All the best :)