Much has been written about the Ender series; many rank it as some of the top sci-fi of all time. I personally found it a little less moving than many seem to, though certainly still enjoyed it. I think Speaker for the Dead (the second book in the series) was my favorite; I would not recommend anything beyond the first two books unless you simply love the characters and want to continue to see them in new situations whether or not it is surrounded by a good story.

Card is one of the greatest authors of our time, but I think he has more interesting works than this. Nonetheless you can hardly call yourself a sci-fi reader in this age unless you have Ender's Game under your belt.