Honestly, there are two mobile games I've really been blown away by: Night of the Full Moon, and Dungeon Boss Respawned. They're very polished, very feature-complete games that are on the small and neatly contained side. For PC, Bastion is pretty damn good. Dungeon Keeper 1 and 2 as well, but it's difficult to get those running anymore. Raft, Ori and the Blind Forest and Stardew Valley are also phenomenal.

I'm sure there are other small games worthy of mention, but I'm struggling to remember them. I usually play large open world games. On that subject, absolutely try Valheim if you haven't.

I'll be happy to summarize each of these games if you'd like me to.