There are lots of tertiary_links at least in germany in the osm db. With the default imposm template they will not be imported and so these parts are totally missing in the map.
Beside it would be nice to have a separate style for tertiary roads in osm_bright
@ajashton - is this still relevant?
tertiary_links are now handled by the import. Next action here is to style them differently - it would be good to call them out with a light yellow fill.