Huh. I loved Ender's Game; it spoke directly to me in seventh grade. I still think it's quite good, but these days I think Speaker is a much better book. More ambitious, I think, and equally successful.
I thought Ender's Shadow was good, but not great. Couldn't stand Shadow of the Hegemon; never read the third. My ex read it and actually refused to have it in the house anymore when she was done.
Xenocide and Children of the Mind ramble a lot. I was unimpressed with both of them. It's been several years, though; I might like them more today.