Upstate NY/NH/Vermont/Maine

The thousand Island region of NY should not be missed. At least 8 - 10 state parks on the route. All with electricity and water some with Sewer. Try looking at
Wellesley Island State park.
http://www.nysparks.com/parks/52/details.aspx

Grass point State park close to the Thousand Island bridge
http://www.nysparks.com/parks/139/details.aspx

FYI, NY is not part of New England. That said, Acadia NP in Maine has at least one campground that might fill your bill. I believe Lamoine State Park in Maine might also work.

What sorts of things are you interested in?
Commercial: waterparks, amusement parks, shopping?
Educational: Museums, exhibitions?
Recreational: Hiking, boating, biking?

What time of year will also help in suggesting places and activities.

Oh Man - Where to Start...

Unless you have specific ideas where you want to go, I can't help a whole lot. If you can, you should get to Fort Ticonderoga, but if you don't climb well, forget Mt. Defiance. (a great story goes with that.)
That area is loaded with state and national forest. When we camped there, it was pitch a tent time and I never paid attention to RV stuff. Not a lot less than I might pay now. Camping is available all over, but it may be kind of tight in season, I wouldn't know about that.

Be ready to stop and take in the view and also clear the tailback.

Matt

Second Watkins Glen and, Letchworth. If you want to check out Niagara Falls, we suggest Four Mile Creek State Campground. Beautiful on Lake Ontario. RV sites are electric only, but the premium ones back up to the lake. We are in Acadia now. The NP parks do not have electric, so that was a little to primitive for us. We are staying at The Narrows Too across from Mount Desert Island. For the area, it had the biggest sites and is one of the newest parks in the area. Full services, heated pool and super clean. The easiest way to get around on the Island is the Island Explorer and the park is on its route. We checked out all the other RV parks in the area for a return trip back and we would stay at Narrows Too again with the second choice being Bar Harbor Camoground. There is also a very nice and clean family park in Ellsworth called Forest Ridge Campground which is reasonably priced.

Must see Niagara Falls

Letchworth State Park just south of Rochester NY. Known as Grand Canyon of the East.

The Adirondacks are worth visiting - beautiful (eastern) mountain scenery, and there's Lake Placid, site of the winter Olympics twice. Although it's not a state park, the Lake Placid KOA is beautifully wooded and a really nice place to stay. One thing - eastern state parks tend not to have hookups in the campgrounds. Some will have electric, but many do not.

Another possibility for you: Watkins Glen SP in the Finger Lakes region. Beautiful park - haven't camped there, but the Glen trail is amazing.