Gameplay issues

One of the most important part of a game, i think, is gameplay.
Not full 3d, incredible graphic, but gameplay.
Tetris is incredible, Flow is incredible, Caesar IV is incredible, and so on.
Every videogamer have a personal "gameplay" in mind and play games with this prejudice in mind.
But.. how can i think about a gameplay that someone like it?
That's the question for me.

Write videogame, a child's dream, is not simple.. first time maybe. With Jpacman and Cute Tower Deluxe, i've copied gameplay and stop. No thinking about how to have a better gameplay. Sooner o later, i've felt need to think about what i'm doing.
Simple? Sure not!
One million of question in my mind.
So i've started to put something on a piece of paper: terrible idea, but useful.
Next step was to to put something on a mindmap :D

So, first problem is: decide what you want to do! My first suggestion :D