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You've got two trackpads, gyro, 4 extra buttons on the back to bind, and Steam Input lets you make custom radial (or non-radial) menus with entries that can press any keyboard key or key combo for you (which you can bind to the trackpads). It's honestly nothing like using an Xbox controller if that's what you're imagining.

Mario Kart is also a funny example as it's one of the few racing games that makes no use of analog triggers for acceleration, so you really wouldn't miss much playing it on a keyboard.