At its core, IO is a combination of the sensibilities of a hacking game and an immersive sim. Hacking games often provide a digital "space" to navigate, and immersive sims traditionally revolve around a physical 3D space full of systemic entities. By combining the two, we can have a better understanding of both -- the digital space can give clarity to the systems underlying the objects in the 3D space, and the 3D space can imbue the digital space with the context and theming that immersive sims thrive on (and hacking games often lack).
The main loop of the game is defined by spreading your influence over a level by acquiring information. For example: you might find a phone number, which you can then use to access that phone, which may have more contacts, which you can also access. Those phones might have passwords hidden in their notes, which you could use to infiltrate networks, or security cameras, or drones, or doors -- all of which provide more opportunities for acquiring new information and new influence, and so on. Eventually you'll have enough control over the space that you can execute your overall goal. Depending on the level, that might be getting a briefcase out of a window, or shutting down a power plant, or crashing an autonomous F1 car.