Like the title says, let me start off by saying Axis Powers Hetalia is not for everyone. It is not for the easily offended, the overly patriotic, those with little interest in history, or people looking for serious business. Because if there's anything Hetalia is not, it's serious business.
It is, however, a witty, light-hearted look at history and international relations.
If you know nothing about Hetalia, all you really need to know is that it is about personifications of countries. The characterization is based largely on national stereotypes, and how other countries view their neighbors in our world. The anime, though derived from the original webcomic, focuses mainly on the Axis Powers (Italy, Germany, Japan) and the Allies (America, England, France, Russia, China.)
Though Hetalia is not the leading scholarly agent, the author did most definitely do the research, and manages to be both educational, and for the casual or knowledgeable history buff, hilarious. Within the show lie endless Easter Eggs from Historical in-jokes, but you don't need to be a history major to enjoy the show for what it is. It draws some comparisons to the western animation show Hysteria!(If anyone but me remembers that.) But it is aimed at an older audience. Fangirls (or boys, I happen to know a few males who love this series) will find delight in the intentional yaoi subtext, or the innuendos actions of more than a few of the characters.
However, Hetalia is potentially offensive. Though I myself find the antics amusing, others might find the stereotypes that come with the characterization unfunny. The author tried as best to his ability to avoid Ethnic Scrappies and the making extra fun out of certain countries, the backlash is inevitable.
For those who aren't into the whole 'history is moe!' shtick, fandom twists and turns things into their much darker counterparts in fanwork. Use that if you need a reminder, but the show itself is a pleasant diversion from the ugly reality.
Though it's personal opinion whether you think the jokes are funny, or that it's worth all the moe, for those who like this sort of thing you will find you love this sort of thing. For those who most definitely don't, it's worth the look at least. You may find yourself pleasantly surprised.