Hi, Silviu. Here's my critique for you.

For the Arrows exercise, you definitely need to work on getting your perspective correct. I notice that the gaps between your arrow eges don't have much foreshortening to them, and neither do your widths of your arrows. Although there may be a small degree of foreshortening, you should try to exaggerate it a little more in order to show more depth. Remember to think of your page as a "window" to a world. Also, don't repeat your lines when you make a mistake. And keep your hatching lines straight rather than curved.

For Organic Forms, instead of having ellipses of the same degree, you should try to vary them up. When you take an object that's in front of you and you slice it up in parallel segments, your viewing angle of those ellipses are not necessarily going to be the same. If you slice an ellipse directly in front of you, you won't be able to see the face of the slice at all, so the degree of it will be equal to zero. If you slice an ellipse not directly in front of you but on the side, you will see part of the face of the slice, so the degree of it will be greater than zero. If you bend that form more (which you should be doing often), then there will be a greater shift in degrees. Check out this section: https://drawabox.com/lesson/2/5/degree

For Texture Analysis, try not to think about the outlines too much, and instead think about cast shadows. I think it's more helpful to think more in terms of the small forms of the subject your drawing, and then imaging there is light shining on to it. From there, think about how that form will cast shadow onto its surroundings. When drawing the shadows themselves, don't think of them as lines, but instead think of them as shapes. It's sometimes helpful to draw the outline of those shapes first before you fill it in. Also, try to include more shadow in the parts where the individual forms meet and intersect. In where the forms meet, the shadows will generally be deeper. In your armadillo texture for instance, it seems as if you're just putting a bunch of lines in random places. In addition, don't scribble when drawing cast shadows either. When you scribble, you tend to rely on randomness or chaos. Instead, look for a rhythm and observe your reference more carefully. This exercise is mainly about choosing effectively which shadows to draw, and that comes from observing things carefully.

For your dissections, similar ideas apply. Think about the small forms themselves - don't treat them as if they are entirely flat surfaces. In this exercise, now you are considering a three-dimensional form to draw on rather than a flat 2D surface. Because of this, you should be mindful of the curvature - in particular, your elephant skin texture. Make sure that the texture warps along the sides. Don't make it flat-looking.

For your Form Intersections, it is unnecessary to add line weight to the corners. If you do add line weight, I believe you can add it to the silhouette of each form, although I think this part is optional. Also, you can draw hatching lines if you would like to in order to better clarify which forms are what. In additional, you should be sticking to equilateral forms as much as possible. Don't make forms overly stretched in a particular direction. Try to make the length of all sides equal to each other if possible, even for your cylinders. Some of them are overly stretched, and this forces you to think about foreshortening more, distracting you from the main purpose of this exercise (understanding relationships of how forms exist with each other in 3D space). When drawing ellipses, draw through them only two or three times (two is better). Don't draw through them more than that. As well as that, the perspective for your boxes is quite off, as there tends to be an excessive number of parallel and diverging lines. If you haven't already, you should do the 250 Box Challenge. Do this before moving on to the next lessons (get it critiqued too).

For your Organic Intersections, think of each form as as actual water balloons, rather than just flat surfaces floating in 3D space. I see some of your forms that look like that they're going to fall off. Avoid this, and try to imagine what would actually happen to these forms in real life if you've placed them there. If they would fall off, then draw them at their resulting position. Don't make overly complex shapes either. Just stick to simple "sausage" forms for the time being. This means keeping each end the same size, and not making the forms taper from one end to another. Try to keep your forms of the same size, too. Don't have very small ones and very big ones. When you're drawing cast shadows, be mindful of where you are placing them. Make sure it describes the surface it is being cast onto. In the top image, you're treating some of your cast shadows as if they are being casted onto a wall behind the forms. Instead, imagine there's a ground plane below them and draw your cast shadows on there. I should say, when you add line weight to your forms, apply them to parts of the forms where they overlap one another, in order to show what's in front of what. I would recommend doing this (and drawing your cast shadows) after you've drawn all the forms themselves. Make sure you're drawing from the shoulder, just like how you've been using it in Lesson 1. Your contour lines are sometimes ending up wobbly. Instead, make them smooth and confident.

As a final note, you may find it helpful to rotate your images on Imgur. You can do this by using the edit option.