I really like the concept, and how hectic it felt.
If you wanted to expand this concept, I think the hectic aspect could be expanded by having an "endless mode" with randomly generated levels and a certain number of lives. Obviously, it would be pretty complicated to make a random level generator which is also balanced, but it'd solve the problem of having set levels (since currently you can just look at the level, die a couple times, and figure out exactly where you need to shoot, which takes away the "twitch shooter" aspect).
There's also the problem with physics where bullets can ricochet directly back at the player when they shouldn't but that's already been mentioned in the comments.
Overall though it's still a really cool concept, and the presentation is also great.