Quechee Gorge is the standard day trip from Woodstock, and it earns the traffic. The Route 4 bridge gives the quickest view down into the chasm, while trails in Quechee State Park let you approach the river and see the gorge from below.
It is busy because it is easy: parking, viewpoints, shops, and the road all cluster together. Go early or late if you want a quieter look, and take care on the bridge walkway when traffic is heavy.