Both of these dramas show different aspects of youth that are often overlooked by those around them. Park Jihoon stars in them, and he does an amazing job with both characters. The relationships in both are also very intriguing and easy to grow attached to. Weak Hero is a bit darker in my opinion, but I still absolutely loved both shows.
Both revolve around the idea of the afterlife. In the Uncanny Counter, there is a group of people who are tasked with chasing down rogue evil spirits that try to escape the afterlife. The main character is very kind hearted and lovable, making it easy to become to attached to, not only him, but everybody that he is close to.
These two are rather similar in regards to the main lead having sort of beast like characteristics due to their parents. Arthdal Chronicles is also a sort of historical take on the concept as well, similar to Gu Family Book. The main male leads are either Song Joong Ki or Lee Seung Gi, so you can't really go wrong there. Arthdal is on Netflix though if anyone is interested.