I went the week immediately following Golden Week and it was perfect. Crowd levels were low enough that I didn't have to follow my touring plans and didn't have to arrive early to stake out a spot for parades and shows. I could just go with the flow. I allotted two days per park and it was more than enough time to do everything. Weather-wise, one night was cold and windy enough to knock you off your feet, and one morning was a bit dreary and rainy. For the most part it was clear and sunny. If I were to go back I'd pick the same time of year.