Hey Eric! Welcome to Drawabox. I'm sluggy, one of the TAs. It is genuinely such a pleasure to be able to help other people improve and I'm glad it's been working for you! Let's go on over this submission. :)

Lines

Really great start here! Your straight superimposed lines are looking pretty good and while your curved superimposed lines have quite a bit of wobble, you avoid fraying at both ends, which is indication of a thoughtful mark. You can iron this wobble out with the ghosting technique and while you'll be sacrificing a bit of accuracy, you want to focus on flow first. After you're accomplishing a smooth mark, you can begin honing your accuracy.

Your ghosted lines look solid. No consistent wobble and you're pretty accurate at hitting your end points. From here, continue using the ghosting technique to make sure you're hitting the endpoint without over- or under-shooting. This will be important for strengthening the illusion of 3D form later.

Ellipses

Nice work on these. The mark is decently smooth, but I'm noticing a little bit of a wobble on a few, and I would recommend working on your control so you can get your ellipses sitting snugly together in their planes, tables, and funnels. You can accomplish this by using the ghosting technique on these marks in the same way you use them on your lines and drawing through each one a few more times. After you've achieved a smooth mark, you can then work on your accuracy. Just like with your lines, flow first, then accuracy. It is perfectly okay to work on these two elements of mark-making in turn.

As for your funnels, your ellipses have certainly improved, but as you're drawing, you want to use the minor axis as your reference point. Your ellipses should be aligned with and bisected by this initial line. In quite a few instances, you have your ellipses aligned more with each other than this line.

Rough Perspective

Great work on this one in terms of perspective. You keep your parallel lines horizontal with the horizon and your vertical lines perpendicular, which helps eliminate unnecessary guesswork. Likewise, your depth lines are fairly accurate and your sense of 3D is coming along quite nicely.

Small side note: While in terms of line work and perspective, you did a good job here, this is a good example of how over or undershooting your end point may have the effect of weakening the illusion of 3D form.

Rotated Boxes

Really really solid work here. Your gaps are consistently sizsed, you get a pretty standard rotation, and your linework is clean and readable. I will note that your hatchmarks muddy up the image a little bit, since they don't all follow the inner-facing faces of the boxes, but they are still clearly mindfully drawn, which is good to see.

Should you attempt this again, in order to achieve a fuller rotation, you'll want to focus on the VP of the box relative to the VP of the previous box. If you move it along the axes past the previous box's VP enough, you'll get the boxes to rotate rather than simply move back in space. Overall, though, really great work on this challenge.

Organic Perspective

Great work here. While you do have a few convergence errors here and there, that's nothing the 250 box challenge won't help with. When it comes to your lines, try to fight the instinct to go back over mistakes with an additional line. This actually has the effect of drawing the eye rather than covering up the mistake, since it increases line weight. As for the other instances of line weight - I would recommend trying to make all the lines in the box of a consistent line-weight or work towards establishing a hierarchy in your weights, so you can clarify the image.