It proved true for us that the trail is prone to flooding, even it was not rainy weather. [More later] We can also confirm that the reviews that spoke of the neglected state of the second half of the trail proved true. As to the surface: in the beginning it was finely crushed stone and gravel, alternating with hard-packed soil and grass, but later, in the second half, the crushed stone became rougher and rougher, sometimes with pieces as big as a fist: not at all good for even my 2.2" wide tires, let alone Mary's with just 35 Millimeters. The result for her were three broken spokes in her rear wheel and a flat. We also found the second half of the trail way more overgrown than the first, and all bicycling ended for us shortly after we had reached mile marker 5, when there were trail-wide and deep puddles which we dared not ride our bicycles through. The sides of the trail were too overgrown and looked too swampy there for us to try and walk our bikes around the puddles. So we just turned around. As to the bridges: they were well maintained, but I decided to stop before each of them and walk my bicycle onto them as they were not level with the bike path but had steps of 5 to 8 inches to get onto them.
Conclusion: the trail is well worth riding as it leads you through a beautiful landscape, mostly under a great canopy of trees, which makes it pleasant even in the heat of a summer day, but I'd recommend the first half only. After that the surface becomes way too rough even for wide and knobby tires like my Salsa Fargo. The second part definitely needs a lot more care, cutting weeds and shrubs that overgrow it, replacing the way-too-coarse ground-stone surface with finer gravel, and filling the depressions in the trail so that it'll be rideable even after some rain. The trailhead in Poteau [since we didn't get to the other end I can't say anything about the trailhead in Wister] could also be improved: there's nothing but parking on the grass or at the side of a dirt road: a bench under a roof, a water fountain and facilities would greatly help there. But in spite of this, we really enjoyed our ride.
More about our experiences, with pictures, here: