Essence is a very amusing, "getting to know you" kind of party game, and is a lot of fun with big groups of people who know each other in varying degrees of intimacy. Here's how to play.
Send one person out of the room. While s/he is out, pick someone in the group who is the Person To Be Guessed (PTBG). Call the first person back in.
The person who was out of the room must then figure out who the PTBG is. S/he does so by asking each person in the group a question in the form of: "If this person were a _____, what kind of a _____ would he or she be?" Classic sample questions include:
At any time, the guesser can make a guess, although it's considered good form to go around the entire group at least once, thus giving the PTBG a very interesting idea of how s/he is perceived. When done in good humor, it can be enlightening and entertaining. Needless to say, it's not recommended to do this in groups where people don't like each other.
When the guesser has correctly named the PTBG, the PTBG is then sent out of the room, and a new PTBG is selected. The game continues in this fashion until everyone has had a chance to be guessed and to guess, or until everyone gets tired and decides to go to bed.