I have first-hand experience with a firsttimer and Kingdom anime. My wife does not read mange but she loves Kingdom. She can look past the bad CGI because the story is so good and she doesn't know what is being cut from the manga in season 1 of the anime. So I would say from personal experience that it does not ruin it for people who are looking for a great story and wont let the animation quality ruin it for them. That being said if you know the person hates CGI, and especially shitty CGI, then it is definitely a no no.