Rust: The Longest War, by Jonathan Waldman. It somehow makes metal corrosion interesting.

Also Napoleon’s Buttons by Penny Le Couteur, a good look at chemistry throughout history.

Slightly old by now, but Portal and Portal 2 remain two of the best games I’ve ever played. Gameplay is intuitive and linear, and doesn’t require grinding or building up resources. I thought the difficulty increased appropriately as well.