Played this now; parts of it are quite nice, but it does suffer a bit from voids, wallswims and, well, non-existent transitions. The latter are the biggest problem, IMO, because they're not so easily fixed. In some cases you may have to insert an entire, new transition screen, IMO.
Some tips re: transitions:
1.) One method I'm using is to base my designs on two tilesets per screen/area, and do transitions by phasing out just one of those tilesets first (replacing it with a new one). Sometimes I do this little by little, over several screens.
2.) Sometimes a 'geological' approach works - imagine you're dealing with strata/other geological formations of different types of stone or something. Or imagine there's some layering in the (usually invisible, in KS) 3rd dimension - i.e. the 'old' tileset is situated slightly behind, or in front of, the 'new' one.
3.) If you're dealing with a built environment rather than a natural one, an abrupt transition can work, too. But, still, it's better to put that abrupt transition in a screen rather than having it happen between screens. That is nearly always jarring.