Road this entire trail this past week as an out-and-back from Brewster. It's in perfect condition with limited road crossings.
As previous comments noted it's not exactly flat. Signage states you cross the Appalachian Mountains (known as the Taconics in this area)!
In Brewster I parked in Markel Memorial Park which is closer to the southern end than Southeast Town Park. It has a short road hop to an on-ramp to the Trailway.
If you want to take the older section to Connecticut the new Trailway dead ends at Peaceable Hill Rd with steps down to the road. There is an unmarked road section leading to another flight of steps on East Main Street (bypassing an unusable trestle). Note that the trail ends about a mile south of the steps where the trail is being reconstructed (no signs of activity).

Rode my bike from parking lot to about 2.5 miles and then turned around. It is beautiful and a must see. I love that it doesn't allow cars. The views of the mountains are just ridiculous.

I do a lot of running and road biking. This trail is great for both. Rolling hill, scenic, great for distant ride/runs. Construction of the trail was completed Fall of 2020. By far my favorite trail in the capital region

Just tried the trail for the first time doing the first 10 miles from Southeast Town Park. In those 10 miles there was one road crossing and you can still go further without one - I didn't go to the end yet. There is a long gradual grade of about 500' over 5.5 miles but really not bad. There are a few spots with a flat rock as a bench but no bathrooms at all and nothing much around as far as stores or such. My estimate is that trail will be mostly shady before noon but will be lots of sun in the afternoon.

Very scenic trail though residential and park like areas including a nice section through a swamp area - bring your bug repellant.

First off — skip the northern part of the trail from the Hampton Manor Lake area if you are a biker — and start your trip at Miller Road (just of interstate 90). You will be greeted by a babbling brooks, rolling hills, and the smell of farms. As you head south through Nassau Lake you will have opportunities for food and drinks. This is a fun ride.

I biked from Brewster to Poughkeepsie on March 12, once it finally warmed up a bit. There were a few short slushy sections and a head wind, and the trail's surprisingly hilly, but I got to Hopewell Junction in about two hours. There are no services between Brewster and HJ, and the trail feels pretty remote, but there's lots of nice scenery.

This trail is great. There are paved stretches (from East Greenbush to Nassau) with mostly unpaved from Chatham to Hudson (with short stretches of paved in that area). My favorite part is the Nassau area.

Now that most of the snow has melted I ventured East from Greenhaven up Depot Hill by bike. Quite a long uphill stretch. When I got near the top the cooler temperatures and shade kept the trail snow covered. After pushing my bike uphill for a stretch it wasn’t clearing. My goal was to get to Whaley Lake but will have to return when Spring temperatures permit. No regrets fabulous paved trail. It would be a considerable uphill walk from Greenhaven as there is no trail head parking until you reach the summit. Mostly wooded with interesting rock cuts along this section. A few intersecting country roads homes and bucolic old farms, stone walls typical to the area. Well worth returning.

I love this trail in All seasons .... walking, jogging, inline skating or cycling! ......... X country skiing in the winter