Consider taking US-2 if you haven't been to Leavenworth. Again, kitchy town with a German theme, but lots of gift shops, dining options, and much more interesting than what's along I-90. It's subjective, but the scenery along US-2 and Stevens Pass will be better than I-90.

The only exception - don't take US-2 if you're going east on a Friday or west on a Sunday. While I-90 also gets to be stop-and-go during these times, US-2 gets chronically backed up for miles going into Sultan - delays are measured in hours for that on Sundays heading back towards Seattle.