I also agree a lot with those below, love the idea and wish it was explored a bit more. I think a score system would've gone pretty rad with the mechanics if ricochets and consecutive hits before firing again were rewarded. Only bug (?) I encountered was instantly winning after I set the difficulty to hard and shell speed to 10 :P
Otherwise yeah, enemies were very tanky (my arm hurt by the end of the game lol) and I wish you could skip the intro on future playthrus. I really like the idea of modular gameplay in the settings, but I wasn't too keen on doing the intro another time. It's a very cool shift in perspective, going from slow to fast, but still tedious nevertheless.