Maybe it was because I had to turn down my settings to get playable rates, but I love ambient weather. Rain is the most common. I would love to see the game support randomized weather, depending on the map.
Rain can come in as a light sprinkle, a moderate shower, or a torrential downpour. Thunder can roll softly overhead or be rather violent in its rapture. Snow can be of varying thickness and loss of visibility scales with that. Howling winds, rolling fogs, there’s quite a lot of potential to add some ambient immersion.
Geysers spraying mist into the air, turbulent air effects over heated pools of viscous liquid. water-splashing effects based on the size/motion of what disturbs it, steam rising from water pools as hot sources are submerged into them, the variable thud of the footsteps of a massive beast or monster…
OK, wait a minute, I went from Weather effects to visual and sound effects… but you get what I mean! Immersion, baby!