One thing I noticed more after reading through the entire series is that the Greek and Roman civilizations get a lot more coverage than other parts of the world. I'd have been happy with combining those two civilizations into one book, or expanding some of the others. The Persians in particular got the short end of the storytelling because they didn't quite fit into any one book perfectly, except possible the Near East book, and there just wasn't room in that book to do them justice. So most of what you learn about the Persians in this series is from a Greek perspective which isn't exactly unbiased.
But I certainly haven't changed my mind at all about thinking that this is an excellent series for middle school/logic stage ancient history. With the exception of the book on China, the writing is interesting, and in all the books the history is solid and detailed. I know my children learned a lot, and I learned more than I expected to.
Highly recommended.