His biggest problem is his awareness in the pocket. He is a little slow (slower than Relf or Favre), but if he can simply learn when to step up or know how to move out of the pocket when it's time, he would be incredible. A mix of Russell's passing ability and size with Favre's mobility, he would be unstoppable. Russell has an extremely accurate arm when he is confident and calm, but his biggest problems I think are tunnel vision looking downfield and he seems to get shaken up after some big hits and loses his accuracy. Also, I think he tries too hard sometimes to squeeze passes in where they really don't need to go. But as far as raw passing ability, he's one of the best I've seen play at State.
*Edited to add that his best pass in this video is his pass at 2:43. That pass demonstrates how big of an arm he has. Not only that, most quarterbacks struggle to hit the back shoulder flatfooted with no pressure, Russell nailed an incredibly difficult throw off his back foot. You don't see many QBs making that kind of throw.