Your remarkable human brain tracks your game as you play. You feed off of what
changes. Your brain has fun when it is excited.
It is that simple.
Every dynamic variable in the game is designed
to either add to the atmosphere of your game situation or bait you with
incentives to adventure on and level up. These variables, and the interaction
between mobs and players, are the pure gameplay of any game. Most games are
entirely lacking in gameplay, and not very balanced when they have more than
the basic gameplay variables.
So you buy a game. You quickly gain levels and reach
the end. You buy another game. In the end its the gameplay, balance, pace,
and fun adventuring that decide whether your few days with
the game was a good or bad experience.
I wish game designers would focus more on what is fun!