Hey there,
thanks for your post! It's quite interesting to me that you didn't find the rocks repetitive, because they are actually just the same 5 single rocks put together into 3 or 4 different formations and then scaled and rotated in the scene. It's a real advantage of working in a simple, stylized way, because I can make a rock formation very large and place the exact same mesh next to it, but smaller and with a slightly different rotation. Your feedback that it works and doesn't come of as lazy is nice to hear! :)
Regarding the jump mechanics: I was thinking a lot about this during development. At one point I had a jump that had zero "air control", but I thought it felt weird. You jumped and had to wait until you landed to gain control again. Then I went to the other extreme and had full air control for a while, which felt more responsive, but also weird, because you could jump and turn around mid-air, which is a behaviour that I personally dislike in most (not all) games. I settled with a compromise, so you jump and have a bit of control mid-air. I'm still not satisfied with it, though (also because of the lack of momentum that you mention).
The lighting in most scenes is fairly simple. For the exteriors I used a realtime directional light and a few realtime point lights to brighten up a few places. I used Unity's precomputed realtime GI on very low settings, which gave a surprisingly good and soft result. The cave scene is lit by various point and spotlights and there I again used the precomputed realtime GI on low settings to get a soft bounce light.
For the volumetric lighting I relied heavily on an asset called HX Volumetric Lighting. I think it's very easy to use and gives good results, while being not so heavy performance wise. I probably overdid the effect in some places, but I overall still like it.
Thanks again!