Thanks for commenting on my sketchbook.
Looking at your work, I'd say your main strength is in composition, lighting effects and color use. You also have a pretty solid grasp on atmospheric perspective, and I like the translucency you achieved in the waves in the last image of post #3 from May 5.
Your main weaknesses appear to be a lack of control over surface lighting (causing objects to look flat or blob-like), a lack of perspective creating overlaps on the edges of objects (rhythm lines, etc.), and a lack of interesting detail on "hero" objects.
- The rocks on the upper right side of the first image have rim lights on the left and right that don't make much sense in the context of the rest of the scene. The pure black cracks further flatten things, showing a void instead of showng the surface of the rocks retreating into darkness.
- 4th image in post #3, with the reddish rocks. The rocks have strong lighting, but don't seem to do any self-shadowing. Many of the rock layers simply stop instead of wrapping around like you'd expect them to, making things look like a cutout. For example, there's a lack of overlaps in the rock column to the left of the characters at the focal point.
- Creature sketch, in post 15 - the wings on the insect look great, but the rest an overall lack of volume in the lighting. The rest just looks flat. I'd recommend doing some studies from life of shiny black objects.
- The concepts in post #19 are fairly shapeless, and lack detail. I very few identifiable parts in them. These vehicles show no indication of how they are constructed, how they move, how the user gets in, the purpose of this kind of vehicle (military, transport, etc.), etc. It looks fairly amateurish compared to your other work.
- In "To the Ancient Land" in post #2, the obelisk is a clear focal point, but as with other things lacks volume and lacks detail. The lighting doesn't match the structure. There are large cracks, but no smaller ones. There are shapes on the side, but it isn't readable whether this is carved, painted etc. The lighting doesn't do anything to reinforce either one. In one area the shape hangs off the edge.
- Post #26 - "the way of the strong". The silhouettes show no indications of the grooves and cracks, again making things flat. Planes of the rockfaces that are facing the most towards the lgiht source are instead being rendered as dark. If anything it should look more like a rim light.
Overall, I'd recommend doing some detailed still life studies of rocks and concrete, especially rocks with a lot of layering going on. I hope you find this feedback useful.