Lots of different landscapes.

Just did this yesterday (9/14/20) starting from Woods Crossing to the northern terminus at the American Legion then back, going past my parking location to the MA line. From the border up to I'd say the Rt. 202 section, it was quiet, saw 2 people but mainly around the Rt. 202 starting point. Comparing to sections north of it, the southern area is more wooded and a narrower trail but easily ridden with a hybrid bike. Anything with skinnier tires would probably have a harder time for the whole length of it. The northern section was quite busy, many walking, enjoying the weather. It is a little more scenic and the trail is wider. Trail is mainly gravel or hard packed dirt throughout though a little loose sand in the southern section in a few spots but not much. At some trail entrances, there is a sign which gives you some pointers as to what you will see along that stretch, gives you something to to try and see instead of just staring down the path.

I've logged about 20k miles of road biking across the United States namely in WA, MO, OH, PA, MD and FL, and maybe 10% of that on trails. To get to stay 99% of the time on a car-free trail for almost 50 miles (as a loop) is rare- and to have some scenery- is nearly unheard of. Thrilled to be in CT now and using this as my go-to ride.

We rode this trail on 9/12/20, starting at the parking lot on route 63.
Overall, a nice trail, but it has a lot of plusses but also some things that could be considered “minuses” by some.
Plus:
Shaded, pretty sections high over the adjoining forest.
Some nice scenery including horse farms (and horses share the trail, we passed several), plus several ponds. Route goes through the woods the whole way…very little in the way of passes through suburbia.
Not crowded.
Not a huge number of road crossings, and typically with good sight lines.
No big hills, some gradual ups and downs.
Minuses:
Most of the train is hard packed dirt or stone dust that makes for a good surface. However, there are significant sections that are a bit rougher. Some of the road crossings involve a downhill, cross the road, and then an uphill…often with a lot of stone or sand involved. There is a section around mile 8-9(when going West) where the trail follows something like a creek bed, with large stones that make it problematic (we walked this section). There are some embedded stones along the way so you have to watch where you’re going and steer around them..or even walk briefly. Some sections do have some drainage issues, so just need to be careful there. And parts of the trail become more like singletrack. We were able to navigate the entire route with our mountain/trail bikes (30 or 32 cc tires)…I would not recommend a conventional skinny tire road bike here.
Please don’t think the minuses outnumber the plusses here. Overall I recommend this trail because it’s pretty and ridable. Maps are available at the Connecticut DEP website.
Finally I recommend starting at the Naugatuck route 63 parking area…several other posters have noted that there’s basically no parking if you start in Southbury.
Check out the Air Line trail and the Hop River trail, not too far away in central Connecticut, for other options you may want to try.

We started in Walpole at Blackjack Crossing. First few miles were tough! But the remaining 12 miles into Keene were great. Some great views and remnants of the railroad. Some beautiful cuts in the stone. Highly recommend!

Heading south toward the Colchester spur, the map shows a fork in the path that veers off to the left. This doesn’t exit. You have to continue down an take a real left. There’s a sign.

Beautiful views of the river. Asphalt walk/bike way. Ranger on duty at Great River Park boat launch/parking area.

I rode the northern section today. Actually started near the Walpole bridge and rode some other snowmobile trails and some side roads to the junction with the rail trail, then on to Keene. Saw no one until I reached the dump. Trail was a lot of fun, but in much better shape south of the dump then to the north. Very slow grade, north of the dump it was great in places and pretty bumpy in others. I rode a basic mountain bike and had no trouble. Heard there was a bad section somewhere but never encountered anything that was really unrideable except one bad embankment. Trail was also easier to follow and more obvious the further south you went, multiple snowmobile crossings further north. This was the first time I tried this sort of thing and I had a very good time. I enjoyed the terrain and seeing where the remnants of the old line.

The trail is a must do for all! It is smooth asphalt the whole trail. Virtually flat the whole trail. Lots of beautiful spots for photo opportunities. A great little farm store and deli just seconds off the trail to pick up a fantastic lunch and sweets with picnic tables on the trail just minutes away! This is a must do trail. I can’t wait to go back and ride it again.