Looking over your work, I think it's clear that your overall grasp of 3D space, of how forms are constructed and how they relate to one another, is very solid. Your form intersections exercise shows that on its own, with clear understanding of how the intersection lines are to be drawn between different combinations of forms. There are some areas where you've perhaps simplified the more complicated intersections (like the cylinder and sphere here), but all in all you're really showing that you've got a strong understanding of 3D space and spatial reasoning as a whole.

The little thing I demonstrated there about ) x ( = S is one way of thinking about intersections, as though it were a multiplication problem. Straight planes have no curvature to them, so they function kind of like the number 1 in multiplication. ) x | = ). Intersect a flat surface with a form that is curving, and you just get the same curve. Multiply two curving forms together however, and you end up with a more complex wave. This is obviously a very simplified way of thinking about it, but it helps remind us of what kind of intersection line we may expect.

Anyway, this strong grasp of form and construction carries over very nicely into your actual object drawings. You're adhering very closely to the previous phase of construction, never jumping too far from the supporting structure you've already created, and you're never afraid to put down the subdivisions you need in order to find where elements need to sit in order to maintain clear proportions.

There is one key weakness that you are demonstrating through much of this submission however, and I only see improvement on it towards the end: your linework tends to have a lot of shakiness and hesitation to it, where you're too preoccupied with accuracy rather than keeping your lines smooth and consistent. This suggests to me that you're no longer employing the ghosting method as consistently as you should be when freehanding your lines, and instead have shifted your time investment to the execution phase (going slower and more steadily in order to get more accurate lines, instead of putting that time into the planning/preparation phases and then executing without hesitation).

Now of course, the instructions for this lesson do let you use a ruler/straight edge, ellipse guides, etc. so if you felt that having to ghost every line was distracting you from the focus of this lesson, then you should have simply used one of those. Otherwise, you still must apply the ghosting method for every single mark you put down.

Now obviously you are entirely capable of using the ghosting method and achieving smooth lines - for example, the form intersections we see here are mostly pretty good, with fairly smooth and confident strokes throughout. This page however has loads of very subtle wobblings in its lines, which make the forms feel less solid in general.

Similarly, through the first half of your object constructions, there's definitely a lot more stiffness to your lines than the second half - I suspect this might actually not be how you draw your underlying construction however, but instead how you apply your lineweight. Remember that even when adding line weight you should not be tracing over your lines carefully - apply the ghosting method here as you would with any other mark you put down. Also, avoid trying to apply line weight to an entire line or the whole silhouette of a form - reserve it only to clarify specific overlaps in certain limited areas. This is considerably easier to do while maintaining a confident pace to your stroke.

Looking at your last few drawings, especially this wonderful little lighter, your linework is definitely improving a great deal. It was also one where you were considerably subtler with your line weight, so that may be why it is markedly better.

All things considered, your work here is very well done, so I'll go ahead and mark it was complete. Just be sure to keep on top of that linework and don't give into the urge to draw slow-and-carefully or trace over existing linework, when freehanding your lines.