I think Gillies can develop a offensive side. Ive only watched him in two games this year(u18s), and a few times when he was 15, so I am no expert. But he does have terrific hockey sense, and is somewhat of a playmaker. He looked pretty good when I saw him, he made a couple great passing plays and is pretty dynamic.
That being said he has blazing speed, and good size. He is a leader on the ice, and can play good defensive hockey, and can hit like a monster.
I think he may be one of the big surprises of this years draft. I think he has the ability to become one of the best players that come out of this draft year.