Id say they continually go downhill from book one to four, but three (xenocide) and four (children of the mind) were a little more entertaining than two, even though by book four the author really started reaching. I just couldnt accept the whole jane, peter and valentine thing.
Enders shadow was pretty cool, but you wont find any surprises there except for the first couple chapters. Personally, I couldnt stand bean. He's just too calculating and cold.