Fall is the BEST time in New England, but book your campground reservations early. There's nothing to truly avoid except maybe driving in Boston. Yes, there are other places you can go for fall colors (Gettysburg area of PA comes to mind) but New England has soooooo much more than leaves-history, museums, fairs, festivals, whale watching, city life-and it's a very compact area so you can easily visit more than one state. Get your Sox tickets early, too, and be prepared for sticker shock on what it costs. Foliage varies from year-to-year so be ready to possibly drive a bit to see good color.