Game studios will often playtest their game to check many elements of their game before further development and launching. This testing includes if the narrative is engaging, if characters are likeable and if the level of difficulty is appropriate for their target audience.
Different from Quality Assurance (QA) practiced to locate any issues in the software, Playtesters trial and establish if a game is going to be commercially viable. To be a successful Playtester, you will have significant experience playing a multitude of different genres of games across various platforms.
An appreciation for game design, gameplay and game theory will help you not only help you pinpoint issues during testing but also provide you with insights for suggesting improvements that game studios will find invaluable.