This "review" isn't really about volume 4 - I'm writing it after reading volumes 1-4 in a row, and my impressions have blurred together so much that I couldn't distinguish one volume from the next if I wanted to.

A cute story. I'm not entirely sold on the character artwork (as usual for me, I have trouble distinguishing some of the characters, notably the minor ones - give me a panel with some of William's sisters and a subset of their friends, and I'm completely lost), but the backgrounds and props are exquisitely done.
The maid + gentleman love story is not new, as has been noted, and feels a little fanciful to me, but still I root for Emma and William, even if I'm not as engaged as I was (for example) when yearning for Godai and Kyoko.

Kaoru clearly has a love of the subject matter and it comes through, but I was slightly thrown by what felt like an anachronism early on - William with a model airplane in 1895.

So, light and cute and entertaining, but nothing ground-breaking.