I believe play is an intrinsic, important part of being human. I really think Wikipedia has it right:
Play refers to a range of voluntary, intrinsically motivated activities that are normally associated with pleasure and enjoyment. Play may consist of amusing, pretend or imaginary interpersonal and intrapersonal interactions or interplay. The rights of play are evident throughout nature and are perceived in people and animals, particularly in the cognitive development and socialization of children. Play often entertains props, animals, or toys in the context of learning and recreation. Some play has clearly defined goals and when structured with rules is entitled a game, whereas some play exhibits no such goals nor rules and is considered to be “unstructured” in the literature (source).
I think young people (aged 10 to 18) play games because kids are wired to learn through play. I think play is natural, and I think absence of play is really bad for the human soul. I think video games are actually really fun patterns for people to solve.
I also think there is something about pretending to be someone else, in another place, in another role, is really fun.