Probably the great way to understand your own principles, is to look at classic games, that have had strong influence on you. Games, that you consider "almost perfect". For me: Warlords 1, Final Fantasy 7, Quest for Glory 1, Des Blood 4. Also Ant Attack, Doom 2, God of War 1. And they have some similarities - not shared by all, of course, but still recurring themes.
- Enclosure/closedness. I prefer linear stories and closed worlds. I want to be sure, that if I complete the game, I have experienced most things, that there are to experience. Knowing, that I have to restart from the beginning to get another story arc, is source of frustration and often turn me away from the game.
- Less is more. It is a game, not tool - so better to have few well thought out and implemented features, than tons of badly done things. Better a town with 3 buildings and 5 NPC-s, than huge and confusing place. A forest with 3 visually appealing trees, that serve as meeting or hiding spots for quests instead of large number of repetitive and useless trees.
- Easy to play, hard to master. I.e. there should not be important places, stories and things only available for those, who have time to perfect controls. Perfection should be rewarding by itself - i.e. winning sword battle with technique should feel cool but the same thing should be possible with button smashing and health potions too.
- Enjoyable in God mode. Good game should allow player to relax. Game should reward curiosity by unfolding story, not require you to constantly fight to get the game experience.
- Replayable story. This is hard to get right, but I think, that story-based game should be closer to book than to a movie. I.e. present the story in relaxed setting, allowing player to set the pace, focus on details and fill the gaps with imagination. And go back and look again things, that he thinks he missed. But there should be only single story and it should be complete.
- Aesthetics over realism. This applies at all levels - world setup, character design, background stories, behavior and so on.
- No forced moral choices. Player should be able to identify with main character, of course - but other than that, he should not be forced to like or hate anyone. This normally means, that there cannot be single main antagonist, but story should be more like constantly evolving mystery.
Call it my artistic philosophy