Nothing was wrong with Ender's Game. Great book. One of the reasons people dislike OSC (other than his strange personal beliefs he sometimes injects into his writing) is his amazing ability to write a good book and then destroy the original idea with awful sequels. The first couple of Alvin Prentice books were pretty good too, then OSC wrote the series into a stupid mess.
I just finished Lois M Bujold's Shards of Honor: it was pretty damn good. Adventurous and easy-to-read... I'm hoping the rest of the series keeps me as entertained.