A few comments:
I tried it first in Yokohama, Japan, where I have lived for more than twenty years. It worked well. Although most streets here don’t have names, the game called up the names of bridges, highways, and even a moving walkway, which was fun. I then tried Osaka, which I have visited many times, and it worked well there, too.
In both cases, the names appeared in Japanese script, which works for me because I read Japanese. If the OpenStreetMap data for some locations is multilingual, you might want to give users the option of choosing the display language for the choices. Also, you might offer a wider range of landmarks for people to choose from. In Japan, the names of districts, buildings, parks, railways stations, bus stops, rivers, and mountains would be nice to include. I tried Manhattan, too, and half of the choices were numbered streets and avenues, which got boring quickly; the names of buildings, squares, parks, etc. would make it more interesting.
In the two Japanese cities, after I entered my choice, the map highlighted the correct location with a dotted line leading to it; I assume that was the intended behavior. When I tried it for Pasadena, California, where I grew up, and Manhattan, though, that highlighting did not appear and the dotted line just went off to the left side of the screen. I used Safari on MacOS. See the following screenshots:
http://gally.net/temp/yokohama.jpg
http://gally.net/temp/pasadena-california.jpg
http://gally.net/temp/newyorkcity.jpg
Finally, a search box to find the start location would be nice. It was cumbersome to zoom out, scroll from Japan to Manhattan, and then zoom back in.