To make a great stealth game, atmosphere is crucial. Games are about interaction, so if your game involves spending long periods of time crouched behind a box, the world has to do a lot of work to make that experience interesting. It needs to find ways to make you feel like doing nothing is still an active choice, letting you plan your next moves through listening to the soundscape, or making you feel like staying in one place for too long is going to be a bad idea...
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