You see people enjoying different types of games.  Some prefer one genre over another, some people can enjoy a game from the same genre as games they totally dislike.  You can think of games as songs but with a slight but very important difference: music resembles a person's emotions while games resembles a person's personality.

The very good news about this is that there are a lot of studies which explains very accurately the science of personality development and the causes and effects that each type of personality can produce.  (For emotions is more difficult, the studies being made are very ambiguous and they don't produce a lot of accuracy for real applications). 

This personality idea can give developers a very relevant clue about making games that appeal certain audiences.  However, this personality idea also speaks a lot about the same developer's personality and his appeal to the created game.

People has managed to go around the world pretending a lot of things to fit in society.  Pop musicians pretend having popular emotions and popular taste in music in order to sell more albums. 

Game developers can also pretend having a more popular personality in order to accomplish making a game that appeals more to the masses of the people.  However everybody knows this "pop" way of thinking is equivalent to selling your soul to the devil (being the devil a lack of inspiration and innovation). 

If somebody ever wants to create a master piece in whichever is his line of work it is known that he must go for what he knows best... and what everybody knows best is themselves, it lies within themselves, and for game developers it lies within their own personalities.

So why does a person likes playing a shooter better than playing a RPG? Games is an interactive way of entertaining, this makes it possible to directly associate a player's objective in life with what the player is looking for a game. 

If a person likes a shooter it will probably mean he is looking for a fast paced, espontaneous and exciting experience and he is definetely not looking for a deep and meaningful interaction or to discover new things and gather interesting knowledge or reveal fantastic and wonderful stories.

As a developer you will find some kind of relationship with your personality and the games you would like to create.  And if you take time to think a little deeper about it you will notice it is a strong relationship and that your own experiences are linked to your best ideas for game features and experiences you can provide for a player. 

So perhaps a good way to discover a meaningful idea for a game could be by looking at yourself, after all you are the one who wanted to make games at the beginning for some strange reason.