NOTE: I do read/follow the scanalations so while I do not think there are any spoilers, it will probably make my review a bit biased.
The series is definitely interesting and unique, but there really is not an overlying story or plot. You're not really going to find much in plot development or anything, as it is more about relaying historical events with a heavy basis on character relations.
While cute (especially with the Chibitalia moments), the artwork and animation is not really all that special. Also, the fact that it is only a webcast (thus far) is not really helpful.
The voice actors generally
fit pretty well; some people who have read the manga probably had different expectations for some of the characters, but overall they are still pretty good. The ED is also ridiculously cute and addictive.
The characters are really the focus of the series: them and their interactions. While some people find find the stereotypes for the series a bit offensive, it is meant in a humorous way, and every country is pretty much subjected to the same mockery/praise. But it is the stereotypes that make the characters great and amusing, because when you see them you really think "Oh, that really is what I can imagine out of some people from ______."
Despite the fact that each episode is only 5 minutes long, the episodes are extremely amusing. While nothing dramatic has happened yet, the comedy so far has been done pretty well.
However, if I really didn't know much about history, I would not enjoy this series nearly as much as I do. Often it's the small things that make me go "Oh yeaaah, I remember learning that!" that make me smile.
While the series isn't a masterpiece or perfect so far, I find it still really good. Simply because while it is not heavy on serious drama or anything yet, it is very entertaining and simply adorable.
I would not recommend this series to anyone who is easily offended or does not know much about world history (namely around the WW I to WW II era).