This is a major E-W route for the N part of the state. The W end (Burlington to Twisp) is the N Cascades Highway - a very scenic, but heavily used (and patrolled) mountain road accessing North Cascades National Park. It is closed in winter (about Nov-Memorial Day), but because of the major mud slide that occurred a week ago near Oso (very tragic - death toll now expected to be around a hundred) they may try an open it early to improve access to Darrington which is a bit cut off right now.
East of Twisp, it remains a very nice road, although it becomes more rolling and prairie rather than mountainnous. There is another major pass near Republic (Shermann Pass). All the side-roads are typically good....some of my favorite riding is in the back roads in the Colville Indian Reservation E of Omak. There is a very funky cable-ferry which crosses the Lake Roosevelt near Inchelum and the roads in this area are stupendous. Another very well-regarded road is Flowery Trail Road E out of Chewelah.
I'm very familiar with the entire area, so ask specific questions if you want more information.
- Mark