For me current chap is FTL: Faster than Light
The two things that keep me coming back are the rhythm of it and the way my brain has just the right amount of difficulty choosing a path between the sector nodes.
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Goof Troop. It can be finished in two hours but so much quality is contained in it, each of the five levels have unique things. You gotta play it with two players though because the teamwork that's involved is the whole point. This is my go-to netplay game, it never tires.