Nan has a lot to offer and is sort of a hidden gem (in my opinion).
For the most parts most of the mountainous roads are in good condition but be careful of other drivers. Thais are known to pass on blind curves and cut across the line when making turns or going around a curve.
There are tons of coffee cafes throughout the mountains where one can stop, enjoy a drink, and take in the fabulous scenery.
Take a trip to Bo Kluea, visit the salt wells, and travel the infamous '3' highway going there.
Or perhaps venture to Pua and visit The Mushroom Farm to have a great pizza lunch.
Personally I enjoy the Nan area much more than Chiang Mai.