What qualities and skills should a great graphic designer have?

I agree with the person in the comments creativity is everything to executing a perfect idea!

for me they must have creativity and some marketing skills

Whatever you do, don't follow the hot new trend of "alegria" art or even minimalist art in general. It looks cheap and tacky.

they have to be extremely ocd, i think a lot of people don't realize that

creative, original, and hardworking

Once, you are in the business, having the ability to actually understand what the client needs, instead of just making what they say they want. Get down to the root problem.

I think Creativity is needed

creativity, consistency, a good learner, have a great vision overall

The most important part - CREATIVITY.
Skills u can learn it. Creativity born within the person. That will separate good designer and brilliant designer

I really think it has to do more with your background, I mean there's just talented people sometimes. But good design comes with good background i.e. Art history, Cinema, Painting everything that "lurks" around image will make you a better designer and overall creative person