Both are thriller/suspense dramas in a criminal/detective setting. They both are looking for a murderer as well as there is the female and male pair in both dramas.
The male leads have different character however; in 'voice' the male lead tends to be impulsive and reckless while in 'stranger' the male lead is phlegmatic and logical at all times.
In 'voice' there is a supernatural element as the female lead has special hearing abilities.

Both of these dramas explore the issue around child abuse and neglect as well as the struggles of motherhood.
Obviously there are differences, where in 'mother' the main character kidnaps a child who is abused and attempts to protect her. It is a thriller and suspense drama that pulls you in.
In contrast, 'the house on the slope' is a drama that gives an insight on the psychology of a mother who has abusive behaviours and thoughts.
They are both amazing dramas so I would definitely recommend!

Both dramas explores the adult relationships between a military soldier and a successful woman. Both female leads have a similar character as they are self sufficient and are able to care for themselves. Both pairs have amazing chemistry and has a good amount of comedy and romance. There are really heart touching moments that can make you cry in both dramas.

Both drama's explore the personal struggles of adulthood. They both give an insight on the struggles of a woman against society and the perception on how they should be living their lives. Both main female characters live together with the male main character as well as focusing on other supporting characters that have their own struggles.