Having lived in NH all my adult life I will tell you that IMO it's about the ugliest time of year. Trees still bare, "rotting snow" still around as well as a good chance of significant snowfall, freezing night temps, mud, frost heaves and potholes. Same for most the Northern New England area. Not to mention very few CG's open but there are some. Don't want to be negative but...
Have to agree even in MA. We still had a lot of snow on the ground that time last year and a number of campgrounds that usually open about 4/15 (Cape) had to delay their openings because of snow. May is usually better and many of the campgrounds have opened by then but if winter and spring run late, May can be cold and wet.