I looked up the guidelines for Doak 7s and 8s, and found this:
7. An excellent course, worth checking out if you get anywhere within 100 miles. You can expect to find soundly designed, interesting holes, good course conditioning and a pretty setting, if not necessarily anything unique to the world of golf.
8. One of the very best courses in its region (although there are more 8s in some places and none in others), and worth a special trip to see. Could have some drawbacks, but these will clearly be spelled out, and will make up for them with something really special in addition to the generally excellent layout.
From everything I've read on this website, it seems to me 8 applies better to Riv than 7, especially based on the last part of each definition. I've only seen it from the gallery, though.