Well, it has few bugs. Or, perhaps, it wasn't meant to be used outside of the US. Compare this:
http://maps.stamen.com/toner/#17/49.19512/16.60929
(I guess I could just fork it and try to fix it, but I'm not sure how. I wish there was a tileset that wouldn't give so much prominence to the roads, but rather to the aspects that matter in the city. Important buildings and landmarks, foot-only pathways, public transit lines. Freeway is just an obstacle.)