I don't think you can really comment too much on a script for a movie in a language you don't know, translations could do a lot. Never seen I Am Legend and that guy supposedly working on the screenplay really hasn't done much so I can't comment about him. As for the plot, you can't really say it'll get massacred just yet. You can say what you want about Speilberg, but there is no doubt that his movies almost always do well, rating wise and profit wise.
and I think Will Smith has proven himself as a serious versatile actor and can do something with this.
But I think if they were going to a remake of a Korean movie. The Host would be right up Speilberg and Smith's alley. You got epic monster movie director and a funny actor right there.