Congo

Definitely not! You're not wasting your time on terrains, Jesuis. This is a good start. I won't repeat on what David said. I just add, that you should soon start experimenting with materials. Just a few hours ago I drove through a landscape, that has some similarity to this one (Alpes Maritimes in Southern France), except for the material.

It's a good start, however, I believe that an image such as this would benefit from a bit of foreground action. For example this scene is designed to give the impression of trees seen from a distance so perhaps this effect could be enhansed by the inclusion of some foreground foliage to give the viewer the feel that they are looking across the canopy, across a valley, across some mist (a good place to hide the transition between foreground detail and background terrain) and widen the camera angle to give a sense of scale rather than the standard view which is rather confineing for this kind of scene - it sometime helps to produce a letterbox shaped scene for that extra panoramic impact too.