overall the map is very good for a first attempt in UE4 however the terrain geometry just feels unnatural in may areas (the wyvern trench is an example, its too geometric and "square"). you need more variation in the base shape and more detail to the surrounding area. additionally the terrain textures are over repetitive. again, more variety will help to break up the repatition and make things more astheticly pleasing as a result.

the caves feel very much crafted as well and need more variation in their shape, particuarly the ceilings. reference material is crutial, look at other maps as well as real world locations to get inspiration and ensure your environments are beleavable whilst also being creative with it and not strictly conforming to the laws of physics in all cases (an example is floating islands or structures that would never be able to realistically support themselves without breaking)

as a whole i like the map but in future maps try to keep these points in mind ;)