I did this trail end-to-end yesterday as an out-and back from the southern end (no official parking at the trailhead but two supermarkets nearby could be utilized).
Overall in good to very good shape.
The non paved sections are OK for all type bikes except perhaps not for road bikes if the trail is wet.
The on-road sections are generally well marked by Empire State Trail (of which this trail is a part) signage.
Informative signage along the way.
It's not exactly a flat ride. My cycling app had it at over 1800 feet of elevation gain for the out-and-back.
Tip: About 6 miles from the southern end is the Hudson River Skywalk over the Rip Van Winkle Bridge with great views of the Hudson River and the Catskills.

As you come into Utica, there is a construction area that would benefit from some temporary signs. You ride down a small hill into a wide open area. Once you do this, you will find that there is no sign that should direct riders to go left. Going left will take you across railroad tracks, and to one of the locks. You cross the lock and rejoin the trail. If you make the mistake and take a right instead of going left, you will be forced to ride into Utica on a busy road. Other than needing a sign at this location in Utica, the trail is amazing. We road from Syracuse to Albany.

We biked the newly completed Under Mountain Road to Millerton. We have biked the other completed sections in the past and this newly completed section does not disappoint . Very scenic and easy ride with our hybrid bikes.

Well Maintained trail as we biked the central to western end. We would have biked the eastren side but it was closed for a maintenance reason. Turned out all the better as most of the scenic overlooks were on side we biked. Our hybrid bikes handled the packed stone trail very well. Would certainly return again

Loved this ride. We rode from Columbia Plaza in EG to Nassau and back. Casual riding took 1 1/2hrs to get to Nassau (and much longer to get back- as it was our first ride this year-do we were tuckered out!). Lol. Miller RD (exit 10) Schodack has a convenient store which is about 1/2 way. So a great “pit-stop”. As was “smilees” ice-cream in Nassau and a Taco place “Diablos ?”sp across the way in Nassau.

Great early fall ride. Amazing views on Mount Greylock and Lake Berkshire. Mostly scenic and quiet. Nice place to stop by the water and take in the scenery. Well paved, wide, smooth ride.

Had a very nice ride yesterday. The trail is well maintained and wide enough that you can pass safely. They are working to extend the trail into Pittsfield. If you find blinking tail light please let me know. Mine fell off my ¿! ¿

My wife and I tried this trail because it is a fairly short drive to Hoosick Falls. It is NOT your typical bike trail. It is gravel (hard packed crushed stone) but not difficult to ride on. We parked in a lot in town at the middle of the trail, rode north which was very nice and not too long. The north end is a bit desolate. We rode back and attempted to continue on the southern part, however it was not marked at all and we could not find any visible "access" point. We eventually made our way through the town and found a sign pointing us toward the trail.
This eventually brought us to the southern end of the trail near some little league ball fields. We rode northward again on gravel for about a mile when the gravel abruptly stopped. We spent 5 or 10 minutes contemplating whether to continue or not. Ahead of us was just grass, but not something that looked like a trail. After about 100 yards it became a mowed grass path which was definitely an old railroad bed, rather high with the river to our left and a ditch to our right. To say the least , it was NOT what we expected. This section was directly behind peoples homes and we were not even sure if we were on a trail at this point. It eventually went under a train bridge and came out where it was not marked at all, a few blocks from where our car was parked. To say the least, we wish we had read a review similar to this so we would have known what to expect. Hopefully this will help to inform someone else in the future.

This was moderate to difficult. But I am in my advanced 50s and over weight. It is 85% uphill, a lot of rocks. Not sure if all the rocks are from hurricane Irene or if it has always been rocky. A hiking stick was helpful for balance. My husband, same age, not over weight found it moderate to difficult, but navigated the rocks much more easily. The falls are incredible! Worth the hike.