I took a run up Success Pond Road today 5/26. As Bryan mentioned the first mile to the ATV parking is rough with cobble sized rocks all over the road. You need to watch the sides of the road as, the culverts are lifting up and have been caught by the road grader leaving sharp pieces of metal in a perfect spot to slash a tire. The road gets better past the ATV area but in general it is maintained for large logging trucks. Those with small cars should plan on no more than 20 MPH. Occasionally where repairs have been done, they have used very heavy agregate instead of gravel. Its passable but will remind you of the begining of the road. There are piles of trees and possibly active logging along the road in spots so if you are going during the week watch out for trucks and equipment. All of the traihead signs along the road are in good shape. Between the Notch trail head and the Speck pond trailhead the road splits in a "Y", the road condition is better on the left side of the Wye, but the Sucess Pond Road actually goes right. After the split the road gets a lot better. It is graded for cars, I went past the Speck Pond trail for a couple of miles and was planning to go all the way to RT 26 until I lost the brakes on my truck. If the road from the 18 mile point continues are good as the section after the split I would recommend accessing the area via RT 26, as if you have loose parts on your car or have your wheels aligned, the drive in from Berlin maynot be kind to your car.
I ended up driving back down the road slowly in 2nd gear and used my emergency brake as needed to get back to my house in Gorham.
A general observation on the road is that it appears that the current owner, Dillon, is doing the bare minimum to keep the road open for trucks. Rather than bring in new material, they appear to be just smoothing out the road without bringing in new gravel. This is exposing the road base and many boulders as well as removing the cover over the culverts which causes them to work up out of the ground more rapidly