This is a relative close match up in my opinion between two very experienced fighters. Roy Nelson of course is a very well known name having fought in the UFC for years. He is mainly known for being extremely tough to finish and having huge power in his hands. Technically he is not superb and not extremely fast, but his warrior attitude and power (as well as his looks) make him a famous name.
Volkov is the less known fighter in this bout, having spent most of his career in Bellator and the Russian M1 promotion. Volkov is a huge heavyweight (201 cm or 6 feet 7 inches) and uses this in his advantage. He has a 20 cm advantage in height over Nelson and a 20 cm (9 inch) advantage in reach too. I think he will use this huge advantage against Nelson but not having enough power to finish Roy Nelson.
I see huge value in Volkov by decision @ 3.25 with William Hill and recommend playing a big bet (8 units) on it. You can sign up for William Hill by clicking on the banner below (for which you might need to disable your adblocker for this page).