With the marker the things that stand out to me are mainly the primary highlight on the right side being a little rough and inconsistent. In the original, it's a pretty solid, straight line, but in your study it's very rough and textured which makes the surface feel a little off. Also, with the grapes, I think you struggled a little getting just the right value range. I can see that there are shadows and highlights where there are supposed to be shadows and highlights, which is more than I might be able to manage. However, some of the shadows aren't as deep and highlights not as bright as they should be. I think this can happen when you focus too much on a local area of the picture; it's very important to keep your eyes moving and keep an eye on the whole painting. Even though we're working digitally, I sometimes like to step away from my computer, even going back to the opposite wall of my room to look at a piece to see the big picture. Nice work! I know it's old, but I help this helps someone.

You matched these very well. If you want more subtlety look at the values of the darks on the green cylinder and the hue/value of the triangle to the farthest right. Keep making awesomeness!

Very nicely done!

Again, great work!

That's so cool! Would hate to see one of those in a dark forest

Nicely done!

Nicely done! Yes, the point of painting should be the art rather than the tech, so I am glad you're enjoying the simplified process

Nice! You got the main values correct and have good soft gradients all while keeping sharp edges to the sphere.