This is a pleasant escape from the city, largely running along the creek and through woods, but occasionally popping out and paralleling residential neighborhoods. There are also hiking paths off the trail.
I love that it's a full loop (no backtracking!). It's well-maintained and quite flat, so it would be appropriate for all abilities. The southeasternmost extension (behind brewery and post office) is not as well maintained.
The northwest end of the trail (off Harford Road) is about a block from Lake Montebello, which has bike lanes running around the lake (and, as of May 2020, the roads around the lake are temporarily closed to cars). So Herring Run + Lake Montebello forms a pleasant, no-backtracking, extended loop. Also, as of May 2020, Harford Road is under major reconstruction, so finding the entrance to the trail from the Lake Montebello end is a little tricky (there's a temporary path carved out that's quite rugged and may create accessibility issues for those with limited mobility).

I have been enjoying the C&O Canal towpath since I was a boy -- but I went for a bike ride yesterday (May 10, 2020) at the Monocacy Aqueduct and the path is now paved (I assume it's considered crushed stone). Yep, it's now "new and improved" -- not. One problem is that the trail now has a lower shoulder than the paved road. If you happen to get too close to the edge or pull off, you've got a bit of a dropoff which could be problematic. Another problem is that some of my fellow bicyclers seem to love the new surface as they now go flying even faster than before. Hiking on the paved trail is certainly not as nice as the previous dirt path. The feeling of getting away from it all has diminished and the trail has lost some of its charm. It no longer appears to be a path in the woods from a bygone era, but simply another bike trail. Pedestrians beware.

Even on a COLD WINDY May day, there were lots of walkers, joggers, and some bikers. Steep on either end of the trail and I’m guessing 6-8’ wide so 2 bikers can safely but SLOWLY pass. Lots of smooth, elevated trail & bridges (lots of warning signs “Slippery When Wet”) Would be very nice in heat of summer since it’s shaded the entire route & alongside the stream. Trail is in the floodplain so would not be advisable when streams are up.

This section is complete. Paved and spacious. Not much elevation but good for a jog with a stroller from one end to the other and back. What’s not to love? Parking ok Crownsville is limited (two larking spots, 3 including a handicap spot) but the Rt3 lot near end of Millersville Rd has plenty of parking.

Got on part of this trail, while on western Maryland trail

After reaching the eastern terminus of the Great Allegheny Passage, I picked up the C&O Towpath in Cumberland, MD back in 2018 (perhaps the Towpath has improved since then). Unfortunately, rainy conditions really seem to impact this path/trail more than other trails. Its gravel surface (which rides nothing like the crushed limestone of the GAP) was a mess back in July 2018. Rain aside, this trail is really, really bumpy which really had a negative impact on progress (I usually tour around 15mph, and struggled to make 9mph on this path). As soon as I had the opportunity, I departed this path for the Western Maryland Rail Trail without any regrets. In my touring experiences, the conditions on the C&O Towpath were some of the worst that I've ever encountered. It's truly a shame: this path would be so much more enjoyable if it were better maintained.

Have done this a few times. I enjoy having this much mileage available without having to interact with cars on the road. And nice access to additional trails connect to this. Well maintained and a great trail for base miles if you don’t want elevation gains.

My wife and I just got “real” bikes and for Us it was great. Well kept trails and paved all the way. If in area it’s a must.

Nearby but feels far away. Flat for kids and pets.