Ended up doing two small hikes at Great Swamp as we had a busy weekend and only had time for a short hike, need one under an hour away.
7.25 miles total (approx., our GPS decided to drop us at end of hike #2) 1st hike: 2 miles, 2nd hike: 5.25...probably. Terrain is level, very easy to easy.
We first stopped at the Wildlife Observation Center and walked the 2 miles of boardwalks through th swamp. There are several observation blinds to check out wildlife. It was mostly shady and the walking very easy on boardwalks or graded cinder beds.
Observation Center trail
There is a kiosk here with a printed map, and an info center with brochures, as well as bathrooms. (online map/directions)
We then drove a few minutes down Long Hill Road to the Blue Trail's small lot. We intended to follow the route in "Hiking New Jersey" so we'd printed out the map detail from the book... which turned out to be wrong... in distance and the map.
Overall: The hikes were a mixed bag for us; the 1st hike with boardwalks was pretty, probably good for kids, but not really "hiking". Blue Trail - a lot of it was just easy, level, hiking through not-that-scenic forest but then you'd come on an interesting or really lush area.
Our full blog post is here, and hike info/photo/video is on our Great Swamp page.