You'll might need a MA orv sticker. I've heard that you are supposed to be okay with a street plate from any State but the policia aren't always acknowledging that and might bust your balls.
The parking lot side at Freetown is typical public riding and can be crowded on the weekends with the usual idiots doing donuts and wheelies near the parking area.
The other side of the road has a nice/tough 13mi. single-track where you can get away from the posers/yahoos. Lots of "baby heads" (small, round, 1/2 buried rocks) to keep you on your toes.
There's also Wrentham SF. Lots of rock and ledge.