What I like most of Puffie's sketch is the tree, because that comes with the idea of having and outdoor part. I think you should really add that as well - however, as a minor part. Like in most tilesets, the greatest part is outdoor with some tiled background indoor stuff, and in your tileset it could just be the other way around. It would be cool to have some outdoor stuff, like a ruined old mine entry and deserted land before that etc.