The word that comes to mind when looking at Harper's Quest is "Cozy". The layout is large, clean, and inviting, the artwork is warm, friendly, and consistent, and the whole thing oozes a consistent tone that says "Climb down into a basement and explore this damp dungeon".
Any game with a grappling hook is off too a good start, and I really just can't emphasis enough how much I love the aesthetic of the large text with the clean, almost-painted drawings. The game is simple, at just 9 pages, but it does what it wants to do perfectly, and that's emulate an OSR-like experience in a nonthreatening and, well, cozy way.