I love Hetalia: watched every episode and the movie, listen to the music all the time, and am planning to read trough the manga and webcomics too. It inspires me the same way Mario does, with how it's pretty fanciful and leaves tonnes up to the imagination even when providing so much material to enjoy. The characters are all pretty likeable except Sealand and there's lots of fun to be had, with the few bittersweet stories mixed in with the humour giving the series heart. It gets flak for being so breezy about things like war, and ignoring some of the nastier points in history altogether, but some fans do find the enigmatic series thought-provoking and there are some pretty devastatingly melancholy art and tributes and whatnot out there if you look.
However, you really shouldn't use it to learn history, because it takes a lot of artistic liberties and simplifies things (and starry-eyed fans saying "I know history because I watch Hetalia" is actually one of the reasons the fandom gets so much rabid hate around the internet, so be careful). But I know for me, it's made me want to learn the actual histories behind the fiction (and about geography, language families, flags, cuisine...) - not only to make sure I don't end up believing misinformation, but also because knowing the full story helps you appreciate how clever some of the plots and jokes are.
=Watching