Well it does not look the exporter will export this scene.
1… The Shaders… The scene is using some custom Vender Shader with funny swatches at the textures. The exporter will try to convert everything (that is can) to either a BABYLON.StandardMaterial or a BABYLON.PBRMaterial.
It always best to use Unity Content that uses the Unity Standard Shaders … Custom shaders are not guaranteed to convert picture perfect. You should change the shaders yourself in Unity. (But remember that custom shader from your scene uses a texture with a bunch of color swatches… You would need to create a custom shader that uses the swatches texture as well… Would probobly have to use the Unity Custom Shader in HLSL as a guild to writing your own custom BABYLON.ShaderMaterial)
2… The exporter dumps out your terrain assets. You must create your ground and handle the Terrain shader yourself… Its kinda complicated to do multiple texture tiles. Especially more that 3… Thats gonna mean a Terrain Texture Atlas, And Splatmaps, Etc…
There are some threads on the forums we have that goes into the details of terrains and texture atlas… Luckily my upcoming toolkit has a Pro Terrain SDK that will be available that will handle this out-the-box (Does not support Unity Detail Prototypes Yet… Like spreading grass and rocks with the terrain painting tools… But is does handle the built in Tree Painting)
3… I don’t do water yet… Gotta look into that one
In summary… That seen is way to complicated with LEGACY and CUSTOM Unity Shaders… Try and use more Modern Unity Friendly Scenes that utilize Unity Standard Shaders or at least that will convert easily to a Unity Standard Shader.
Sorry bout your scene for now