Decisions in game design

One of the big problems in development for me is the game design. I have a habit to leave some things later and then realize it has been two or three years since I tried to solve some design problem. In roguelikes there are lots of problems related to RPG system and how to create interactions between objects. I think we all would like to create complex interactions, but it requires more generic and able engine. Limited actions are much easier to do, but it's including a decision to create a limited gameplay rule. I know that I have to make those decisions or this game will never be released.