I rode Morrisville - Black Eddy - Milford - Trenton this week (PA side going north, NJ side going south.)
Decent surface for the most part on both sides. I rode 35mm road tires on a cross bike, and felt a little beat up by the end but it was completely do-able. The PA side is somewhat rougher but more scenic.
There are closures on both sides. PA side, the Tinicum Aquaduct is closed and you'd need to jump onto PA32 (River Road) for around a mile before getting back on the towpath. NJ side, the towpath is closed south of Lambertville. If you decide to go that route, either cut over to Route 29 at Bridge Street (rejoin the towpath a few miles south) or alternatively, take the bridge to New Hope and go down the PA side. No more issues in PA between New Hope and Morrisville or the Calhoun Street bridge back to NJ. I'd personally choose that option, since-- see above-- more scenic. It takes you past Washington Crossing State Park, the Soldiers' Graves near the trail, and follows about four feet off the feeder canal.