I do Creative iMedia and Computer Science for GCSE - here's what I think. I HATED CREATIVE IMEDIA! I didn't know it required so much drawing, I achieved under my target grade for my first unit. I LOVE COMPUTER SCIENCE! For Computer Science I get grade 7/8/9's. For game design I would suggest Creative iMedia - but it also depends on the units your school chooses - I wouldn't recommend it if they don't choose the game units but it's better than if you chose graphics for GCSE. Computer science for gaming would be irrelevant - too much unnecessary content which wouldn't be helpful.
Hope this helps. 😊