Dan the Man

I am a huge stickler for immersive and ambient sounds in games; it helps sell the whole experience. A great example of what I mean is The-Between-Lands mod for Minecraft. There's a symphony of noises and animal sounds that brings you to that place and surrounds you. 

I don't know if some of these are already planned/implemented.
Some specific things could be:

• crickets/cicadas chirping
• frogs bellowing
• bugs in swamps
• birds songs
• water dipping in caves
• echoes in caves
• sticks cracking when you step on them
• wind rushing over mountains
• larger wave sounds for larger water bodies
• trees creaking in the wind
• rattlesnakes in desserts
• loose pebbles falling in caves/mountains
• etc.

Basically whatever animals aren't added into the game, make them into environment sounds, and more auditory cues from the diverse landscape.

loving the game so far! :]