I saw Rogue One with very little Star Wars background. Going in I had no idea who this character, or actor, was. It was definitely not immediately obvious to me that this guy was CG. I did eventually realize there was something off, particularly in the scenes featuring him with Krennic. I thought maybe these scenes were just weirdly lit, or that maybe either Tarkin or Krennic, or even both, were CG (it seemed a weird idea that they would CG I guy I knew to be alive and well in Mendelsohn but I really couldn't tell, just knew there was *something* going on).
Anyway at the end of the movie I had to Google it to be sure what was going on. Obviously most who knew the actor and the character would realize something was up and would start trying to look closely for flaws. My partner on the other hand had a similar lack of background to me and had no idea that wasn't a real guy.
So pretty successful digital recreation I'd say. While not perfect, still one of if not the most impressive I've seen. I do remember young Michael Douglas in the opening of Ant-Man leaving my jaw on the floor though, which is perhaps my favorite example. Though I guess having the real actor, albeit aged, available helps a lot.