I tend to play a lot of Minesweeper ( https://polytoria.com/places/10906 ), but I find that Cabin Hangout ( https://polytoria.com/places/91734 ) is quite nice for just chatting with people in game (outside of Hazard Survival of course). I also stumbled across a WIP game called London Simulator ( https://polytoria.com/places/96871 ), which while it is somewhat barebones right now, I found it very funny. Blade Fights in the Heights but better, let me tell you.
I haven't quite found any super entertaining single-player games on there yet besides Minesweeper (well technically it's multiplayer but you don't often see people in there so shhh), however: the games I've enjoyed on Polytoria so far mostly have some sort of social tie-in. Now, I'm not sure if it's purely because of how rudimentary and difficult to use the studio is (or so I've heard) or if there's some other reason to it, but I do hope that at some point some enjoyable single-player games will come along that aren't just obbies or tycoons. Or maybe I'm just extremely blind, haha!