[somat]

Perhaps the best way to get started in the rather complicated world of game design is to make a mod. That is start with an already completed game and modify it to your will.

These game engines should probably provide something like this. Something like here is "Generic FPS" the game sucks, but it is a complete game with all the moving parts plumbed and licensed that you are free to use it as a base for any game.

A free rant on engines.

A game engine is roughly the same thing as a web framework, that is, it is an outer support layer with well defined exit points and you have to provide the business logic yourself. This works in conjunction with libraries which are inner support layers with well defined entry points and you have to provide the business logic yourself. I always preferred the term engine more than framework and always wondered why it was only used for games.