I originally read about this trail on the internet. While traveling through the area I stopped off to bike it on an early morning in 2007. I parked at the southern trailhead, biked to the northern end, and then pedaled back to the southern end.
The trail is very scenic and runs through a nice area which is by turns a small town, and then rural. An interesting feature of the trail is the tunnel which occurs near its mid point. The tunnel was originally a rail tunnel, and has been adapted to use as part of the bike trail. The tunnel is rather short (a few hundred feet), which means that you don't need to fear that it is dark. It is rather cool (temperaturewise) and moist in the tunnel, which is a welcome respite on a hot day. Another review mentions that the tunnel is wet, but I didn't find it to be a problem.
Personally, I also enjoyed the cow farm visible off the trail's northern extent, but that's 'cause I don't see farms very often since I live in a big, dirty north-eastern city. I thought it added a bit of laid-back rural interest to the trail.
Finally, the town has put a little park with a gazebo located at about the trail's mid point. When I was there in the morning, I found the park very picturesque but deserted. Maybe the residents were still in bed at the time? The drinking fountain there provided welcome refreshment.
In any event, a very nice rail-trail. Bravo, St. Clairsville!