Playing game is very fun filled experience. And there are lot many criterias to evaluate whether a game is a game or not. First of all a competition is not a game. Game have to have element of interaction between player. And the interaction has to be a significant ones. When a turn of one player affects other player's turn it induces challenge and more fun in the game.
Also there has to be an abstract goal and a manifested goal for the game. An abstract goal is something which is indirected e.g. teaching maths and a manifested goal is something that needs to be achieved while playing say in chess you need to defeat your enemy in some condition.
Abstract goal becomes clear as you go further in game design.
And as you proceed further in game design the level of frustration increases. Deciding game plan becomes very important aspect of designing a good game. It can be as simple as stealing treasure from a castle and coming back home. And on it is developed the entire game. You develop rules as you play the game. And this requires at least 5-10 iterations of play. The hardware evolved too. You need to add graphics and styling to the game to make it more interesting and meaningful. Themes in game add variations and charms and can bring fantasy in it.
Right now I'm also in the process of developing a game. And I'm very frustrated. First I am getting lot many ideas of different game plans but not able to concentrate on one. This is because am not able to frame rules for them easily and this results in shift in the game concept. Second, the game that I selected, sir didn't like it. I don't know I need to evaluate the game against the criteria. Though it may succeed the evaulation it has to succeed in making people play.