Death Note is a more serious anime with a boy that wants to rid the world of evil people, the criminals big enough to be on Japan's news. Another boy, who wants to find out who he is, is acting as a detective against the one boy.
Hetalia is hilarious. It's basically pure comedy with the countries of the world personified to people. The different countries look unique and to their culture and act as their cultures as well. The episodes are only about five minutes long, but are so good for laughs it's worth watching. My favorite character here is Germany, or Ludwig Beilshmidt. He's a very serious person with blonde hair and blue eyes who acts a lot like a soldier in every aspect of his life.