Mysterium is a deduction game, which helps to reveal the subtleties of how the other players think. The person playing as the Ghost is not allowed to speak, so the psychic investigators have to try and find any connection between the vision cards they've been handed and the correct choice from a multitude of options.
For example, the ghost can give a vision card that has a red river, a clock, and fields of wheat on it. The investigator then has to deduce that the red river represents the ball of red yarn on one of the choices. But there might be red elements on other cards as well. Or the investigator could choose to focus on the clock, or something else that the ghost didn't mean or notice.
Getting things wrong might not advance the team of investigators toward victory, but it is balanced by the often comedic misunderstandings between the investigators and the ghost.

An excellent example of the heights this medium has reached. All the components and cards look like miniature paintings that are a joy to observe.

You get a lot of high quality components in the box. Various cards, two sets of tokens, sleeves, cardboard templates, a sand timer, and other bits and pieces. The design fits in to the mysterious theme, and nothing looks out of place. This can easily be a game around which you can center an intimate party with friends.

All pieces and mechanics of this game work together in favor of a unified theme, and it works really well. The ghost is not allowed to give any verbal or non-verbal clues apart from the intended Dream cards. The psychic investigators have to get in to the mind of the the ghost in order to guess correctly, so it does feel like mind-reading in a sense. The time limit for each turn promotes a feeling of high stakes, and keeps you on edge- as you would be, if you really were in a manor communicating with a ghost.