Hetalia is a moe-style comedy series that has a very shallow and twisted outlook to its main topic of world history and politics.
As someone who actually cares about history and the human condition that influences what countries and people have done throughout time, I found Hetalia's representation of basically every single thing lacking and shown in a dangerously glorified and sentimental fashion. The style of simplification employed by the series is not one that removes everything extra to preserve the relevant core: instead, it disposes of all substance and deals out half-assed references that often miss the point of the real history and reasons behind them.
I shudder to think that someone might consider Hetalia educational by virtue of its subject matter. If you don't have prior knowledge about something it portrays, all you're left with is a near-unidentifiable mockery completely mangled and disfigured for the sake of cute delivery or some unfunny and shallow joke. The series is more likely to mess up your perspective than help build a realistic understanding of anything. I suspect that Hetalia is especially liable to fuel infantile nationalism and a misguided tendency to see interactions and ethics between nations similarly as between human individuals.
If you want to see a parody starring anthropomorphized countries, the webcomic Scandinavia and the World does it with much more substance and better comedy, and more responsibly might I add.
For me, Hetalia was very lame and unentertaining in its content and delivery, and overall it was very annoying to watch.