I live in Stow and have ridden most of the conservation lands. Rattlesnake is a nice change of pace as fvh420 says, definitely more technical than STF. I like to take my HT on the tour de Stow, starting from ~the Stow Community Park to Delaney through Marble hill, Heath Hen, Flagg Hill, Captain Sargent, Red Acre, Stow Town forest. A little road riding is necessary. You can also venture into Boxborough, Acton, Bolton, Harvard, Sudbury and Maynard pretty easily to add miles on. I can send the URLs to some Garmin track if you are interested.
That "tour de stowe" is called the Stowe's Emerald Necklace. I recently did the hike with my girlfriend which takes approx. 4 hours to complete the entire thing. Very enjoyable hike and nice to see all these conservation areas linked together with a few road section. We had a really wonderful time on our little adventure. The whole time we walked I was thinking how fun it would be ride on a mtn. bike. Trails are not really technical but would be very enjoyable to do for a nice afternoon ride and I can't wait to give it a try. Even just walking I highly recommend it.