Summary: an easily accessed wilderness river that at lower summer flows provides sustained, high quality pool drop boulder gardens. Good packraft flows might be around 200-300 cfs.
Beta: near Ovando, MT, the TH is 12 miles of good gravel road north of 200. 4 miles north of the main TH is the first pack bridge. I floated the ~8 miles of river from that down to the road bridge a few miles south of the TH, then walked the road back. 3.5 hours roundtrip. The gage (http://waterdata.usgs.gov/usa/nwis/uv?site_no=12338300) read 212 cfs when I did it, which it on the low end of ideal. I had pay lots of attention to not get butt-hung on rocks, and purposive ricochets were essential to stay on line through many of the drops. However, provided I stayed with the main current I never had to do more than occasionally butt scoot to make it through, and all the actual drops (save one) had plenty of water and were very runnable. One minor drop just didn’t have a packraft sized gap that I could see, this was the only drop I portaged. Astounding, there were only three river-wide logs, one of which was dinky but at water level and thus required a portage. Another could be ducked under on far river left, and the third was a massive lincoln log construction with multiple huge driftwood logs suspended 10-15 feet above water level. The best and most difficult action came soon after the put in, with the river at its most constricted, though portaging is always easy. A middle section widened and got a little more scrapey, before things tightened back up a bit south of the TH.
I really have no idea how to rate this sort of thing. The low volume and pivoty nature of the boating makes any craft other than a packraft unthinkable, or at least miserable. PR 3 or 4, perhaps? I call it PR fun.