Obviously it takes the percise care of everything involved in a movie for it to turn out properly. However, i have never seen a movie redeemed because the writing was good, or the directing was superb, or because the script was intriguing. A script requires good acting for it to work. A script cannot be astounding on it's own it requires acting to capture the effect the writer was aiming for. I think directing is the overall sum. Bad acting, bad lighting, bad editing and bad writing are usually the result of a bad director. Though, sometimes the director doesnt have much say in the matter, the director's word is second only to the producers. I have seen many movies saved merely by the acting. I think a good movie can be achieved with mediocre acting, but it will be nothing more than mediocre.