It may have been a pain in the ass, but I think overall you showed a good deal of progress. There are some issues I want to touch upon - some of which you may already understand and have learned on your own, but it's still worth laying them out more explicitly to be sure.

The first one I want to address is your tire texture in number 3, specifically how it's got these great big gaps between each "tire tread chunk". This is very similar to any kind of a crack that you might find in a wall or in stone (and so it's present in your dry soil texture in 23 as well), and so it's a kind of challenge we come across frequently. Many students will see these kinds of textures as alternating between positive space (the top face of the tread chunk/form) and negative space (the gaps in between them). This unfortunately flattens out the texture into something of a series of graphic shapes that do not actually reflect the fact that these forms exist in 3D space - and most importantly, those tread forms have side planes to them.

Here's a quick example using a crack. Because we're drawing shadow shapes to convey texture, we have to think about the light source, as the cast shadows are created by the relationship between the light source, the form blocking the light, and the surface upon which the shadow is being cast. As you can see on the left side of the diagram, there's generally going to be some amount of the side plane that receives light, and so it'd be incorrect to just fill in the whole gap with shadow. We need to ensure that the light hits both the top plane, and a little of the side as well.

The second one I wanted to talk about was definitely something you got better at, so I won't dwell on it too much - but in your first texture, the feathers, you kind of "painted" your marks on with individual strokes. This resulted in a lot of contrast even when you got towards the darker end of your texture - a lot of little slivers of white peeking out in between, and really not enough designing of actual shadow shapes. As a rule, try and always approach drawing textural marks (at least when doing so with fineliners in this course) using this two step process. It'll force you to think of everything as a shape, and it'll also help you avoid creating shadows that are just too uniform in their thickness as shown here. You can actually see an example of this through many of the marks in texture 14.

The third point to mention is actually one that is persistent throughout most of your textures. Sometimes you do a better job with it, but its overall prevalence suggests that it may simply not be something you're thinking enough about. In this exercise, we draw a solid, filled bar of black on the left side of the gradient, and we try to leave the far right side an equal bar that is just blank. This is to set up the extremes between which we want to have our gradient transition, and the goal is that once we're done, we should not be able to identify where we transition from these bars into the actual texture itself.

Through most of your texture studies, there's a pretty visible jump from solid black to texture. This simply means that you need to push the darkest, densest part of your texture much farther as you move towards the left side, allowing your shadow shapes to expand and grow. Don't be afraid to let those shadow shapes merge with their neighbours, and to eliminate more and more of the little patches of white. While this kind of issue is demonstrated in these notes (specifically the diagram), you're obviously showing plenty of transition - it's just that there isn't enough on the left side. So be sure to think about that more when handling your textures. It comes in especially handy when we use texture in combination with form shading like this (which we of course don't apply within the boundaries of this course).

All in all you've shown a great deal of progress throughout this challenge and have explored a lot of different textures. Keep up the great work, and consider this challenge complete.