Most notable is that this will NOT be another "Alien" movie. (You could say it will be a "Giger" movie.) The plot is based in the same "Alien" universe as the first film but will divert into its own story - diverting further away from Alien in the Prometheus sequel that Scott has mentioned. He has also said Prometheus is not a true "prequel" because of this.
I'm glad there aren't going to be any Xenomorphs (though, I'm sure there'll be something similar).