i'm so jealous, i wish i could go through them again for the first time. defo have read and re-read them several times.
the main storyline speaker/xenocide/children of the mind is certainly in the hard sci-fi vein... where ender's game is a cool sci-fi book about kids, this is about grown ender being basically a missionary -- like he sleeps on an old starship for so long that when he lands, faster ships have been invented and the legend of ender is ancient history.
the shadow storyline sticks with young peter on earth and basically all the kids from the training program, who become generals of all their nations but they're still kids... so not so much hard sci fi but very fun.
RE: Ender's Game - Fiction that isn't exactly science-y, but very sci-fi due to its themes