This is the headwaters of the Raritan, mostly class I-II. I've never tried above Naughright road, but by the looks of it from the Manor House Road Bridge you'd need a chainsaw and a kevlar suit to paddle down from Budd Lake.
I last did this stretch in an ocean kayak in 92, so I have to check this run out again some day. There could be strainers and various hazards so watch out as usual. Please send any updates.
This is mostly moving flat water, with riffles here and there. However, when the South Branch High Bridge Gauge is at 9-10 feet, you will find some hidden central NJ park and play spots... see you there! At high water, however, there is the danger of low bridges: one definite hazard in Middle Valley, and the Long Valley bridge could be tight, too.
In general, this is a fun paddle for big open boats. Bring your cooler and picnic. The scenery is incredible. The put-in may look a little brambly, but it opens up.
A fun treat is paddling into Long Valley and Califon. The towns creep up and suddenly you're paddling by houses that are built right on the river (from days when building codes were kind of loose). You'll probably want to portage over the dam below Califon (pass the iron bridge and a small lake in town.
The next stretch (Califon to Hoffman's) starts to pick up: more rocks, some class II, and probably more strainers, so be more alert. Take out at Hoffman's Crossing bridge for the end of the run.