Your imgur is not in order, but I'll go through the order of the exercises of the website.

Starting with your organic forms, you aren't quite following the simple forms you should be following. Rememeber organic forms should be 2 balls connected by a tube of consistent width. There shouldn't be any bulging or pinching on them. Check again the page of the exercise to see what I mean.

You are also drawing more than 2 times the ellipses. Only draw them twice. For your contour lines, they look a bit rushed to me, if that's the case don't forget to ghost them until you feel confident. Contour organic forms don't seem to shift the degrees of their ellipses much, so try to be aware of it more, just like how you did on the contour ellipses forms.

For your arrows, they flow pretty nicely. To improve them, you can add lineweight to the overlaps with ghosted confident superimposed lines, and you can exaggerate more how the arrows get closer towards the viewer. Make the space between folds get bigger and bigger as well as the size of the arrow itself.

Textures look pretty good, I can see you are focusing on cast shadows, and that you are looking at your references enough. Though the first texture looks like it might have been rushed a bit. Gradients look pretty good too, with the only issue that you aren't pushing your blacks enough, remember that he transition from black should be smooth.

In your dissections you've done a pretty good job here as well. You've outlined forms in a few of them instead of focusing of shadows, but mostly you're wrapping the texture nicely around the forms and you are making a good use of the silhouette, good job!

Into your intersections, they have issues. The most important one is that you are repeating lines. Only draw through each line once, that's it. You can add lineweight just once to some lines, when they are overlapping, but refrain to repeat lines just because the lines you did before were off.

Don't use other pen with your intersections. It's fine to use a brush pen along with the fineliner. But don't use more than one tool for the same drawing, only the exception of the brush pen

You've got some clear divergence issues on your boxes. Remember that the main objective of this exercise is to draw forms cohesively in the same scene, and breaking the perspective like that breaks the illusion.

If you haven't done the 250 box challenge, you should do it before going on. It's a prerequisite for the form intersections exercise.

Lastly on your organic intersections, you are too repeating lines, so refrain to that. And your shadows are sticking to your forms. Remember shadows should run through the form of the surface that they are being casted on. Think more too about how the organic forms are on top of the other forms.