Gameplay is mostly waiting, not interacting. And how does one use the coins collected? The instructions illustrate the "shotgun" is 750 coins, I've collected over 3,000, and there's no shop.
The shop is on the seventh stage, you can walk freely through each stage ignoring the enemies, and if you kill or hurt one on the way it remembers when you come back. It's open ended, you don't have to wait, you can just walk past the enemies.
