Write down your design pillars. This is the foundation of your game and should never change. Your whole design should tie back to these pillars. It should reflect the emotion you are trying to deliver

My Design Pillars: -

Tension and Suspicion

Players are always second-guessing the opponent’s moves.
Immersive roleplay
Control

Feels like being a manager of a shady hotel in a crime-ridden city. Bribing, lying, manipulating.

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For example, this is for Sub Nautica:

Intoxicating Creation

The overwhelming excitement of being able to build anything.

Thrill of the Unknown

Excitement, dread and tension of exploring the unknown. No idea what dangers/rewards are down there.

Cascading Hysteria

Uncontrollable outburst of emotion, fear, irrationality, laughter, weeping, etc. FTL style chain of "oh sh!t" dependencies, where a failure in one system can affect others, until you're suddenly in trouble.

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Further reading