^ It's both acting & writing really. A great actor or actress wouldn't go as far without someone writing to their strength and a cohesive and interesting storyline.
I'm not certain what you mena by "wouldn't go as far", but great acting trumps bad writing any day. A really great acting performance will make you forget bad writing.
And lets just say that Eliza Dushku had been cast as the lead in Orphan, you think this show would be anywhere near as great or as popular having to depend on it's writing and Dushku's acting? I don't. The writing isn't bad but it sure isn't the draw in this series.