I second Deep Rock. I’ve recently got back into Destiny 2, which could be an option too. But it’s also a lot more than a simple fps. Plus it’s infuriating and addictive.

Functionality, ease of use, and longevity taken into account, I’ll have to disagree based on my experience. Shield, Roku, Apple TV, Chromecast, Fire, Raspberry Pi in that order. But if they’re planning on using it just for streaming, a Roku stick is the simplest, cheapest, and easiest option. And unless they’re already deeply integrated into the Apple ecosystem, I’d avoid it too.