Worth noting:
I expected a significant positive split, after pushing a bit more on the way out for the one-way time, but it was only a couple minutes slower on the return trip. So, if you're going for the one-way FKT, definitely travel south -> north, it's definitely the faster direction. I want to come back for it. ;)
Pretty runnable trail, as others noted... at first I wasn't sure it would be because the northernmost half mile that runs right along the Housatonic is a bit tough, mostly because it's slanted down towards the water but also because it has some rocks. It's a lot like the first mile or so of the Lake Zoar Trail, but not as technical.
The whole trail felt like I had been there before, because it's so similar to Lake Zoar, Pomperaug, and Lillinonah, all of which run along the Housatonic within maybe 10(?) square miles of each other.
Thankful for Grace's note about the road section. It's not well blazed but you just follow the road... I wouldn't have been comfortable with that part if it weren't for the route I had on my phone. I hate getting off route. :-P
Folks who ran this route last summer/fall noted an abundance of downed trees, but they have largely been cleared. There are only one or two to climb over, and a couple small ones to jump over. There is some lumbering in the southernmost mile, but it's pretty easy running there. Just don't twist your ankle in a tractor track.