Hi Pandacatlad, and congratulations on completing the 250 boxes! I will handle you my thoughts on your submission here and divide my critique in two major sections.

Linework and confidence

There's definitely some uncertainty in your linework at the beginning of the challenge, with noticeable wobbling. However you get quite quickly more comfortable once you have acquired sufficient familiarity with your task and by the 50th box or so your construction lines look smooth, confident and quite precise. Your hatching lines however do remain throughout the challenge quite imprecise and curved, as if done without much planning. Remember that hatching lines are lines just like any other and just as them they require making conscious decisions and planning and construction through the ghosting method. Another mistake in your mark-making is the presence throughout the challenge, especially at the beginning, of multiple repeated lines. As tempting as it may be to correct ourselves, in this course we always try to work with or even exploit our mistakes and in fact corrections such as repeated lines often end up actually worsening the situation by making everything messier and making our shapes feel less solid. The only reason we may repeat a line is to apply line-weight to a shape, which is always done through a single repeated line and, in the case of out boxes, only on the silhouette of the shape and not on the internal sides.

Shape and convergence

In this section we begin to look at the aspects that are specific to this challenge. Starting with your line extensions, as you already pointed out we see quite a few boxes with extensions drawn in the wrong direction. The problem seems to be prevalent in the beginning of the challenge and to become less frequent as it goes on, but begins to pop up again near the end of the challenge. Remember that our extension lines are a tool we use to check for convergence and for this reason they should extend away from the viewer, towards our established vanishing points. If, when you have finished a page of boxes, you have some doubts about where lines should extend, do not hesitate to rotate the page to put each box at an angle where things look more clear to you.

Another more structural problem that some boxes show is an inconsistency in your convergence. Two very clear examples of this are boxes 211 and 212: in both of these boxes both of our horizontal sets of sides are extending away in a manner consistent with each other, but the vertical set is actually diverging away from us. According to the rules of perspective, these two and similar boxes do not have rectangular lateral faces, but trapezoidal. If you have difficulty with how to place your vanishing points, remember that a way to tell is from our initial y: if we draw a box from the initial y, the two arms will tell us in which direction we should place the 2 vanishing points for the horizontals of the box, and the leg of the y will tell us which direction for the vertical is consistent with the other 2. Here as well, if you have difficulty to visualize how a box could look like if a y is shaped or oriented in a certain way, it is perfectly valid to rotate the paper until you find an angle where things look clearer.

Another problem that I see often is that you tend to keep your foreshortening very shallow, and while this is not a bad thing in itself, keeping our foreshortening that much shallow in a learning phase and especially while we are eyeballing perspective can lead to some unsatisfactory results like parallel or subtly diverging lines, an effect that is particularly present in the first half-to-middle of your submission. Sometimes your boxes, box 45 for instance, also show a "convergence in pairs" in a set of sides. This is a quite common mistake that often happens when our box has a vanishing point relatively close in one direction but relatively far in another, and what happens if we first traced the lines of the far VP is that, since we are eyeballing, our brain is kind of tricked into making things more even and making our lines less inclined than they should be. A possible fix for this would be probably just to ghost a bit more carefully for each side, making sure to ghost first on the existing sides to remember ourselves where the next lines should go.

Conclusion

I hope I didn't come off as harsh in my critique, but I just wanted to point what were in my opinion some issues of this challenge that are worth a bit more time. Having gone through the ordeal of the challenge I understand how much frustration it can cause and how many little factors sometimes contribute to give us a less than ideal result. Given all of this, I think that there are things worth revisiting but I don't want to load you with too much work, so before moving on I will assign you just 2 more pages of boxes. What I'd like you to do in these 2 pages is this: draw 6 boxes with extension lines in each page as you did in the challenge, but in the first page focus only on making boxes with all of the vanishing points contained inside the page. The VP doesn't necessarily have to sit close to the box, but it should still be inside the page. This way, ghosting with a certain degree of accuracy will be a bit easier and will also make it easier for you to reason on how the form looks and extends in 3d. If you have difficulties, you could also try for 3 (but not more) boxes in the first page to actually place a mark for each VP during contruction. In the second page you can do your boxes however you'd like, with either shallow or radical foreshortening, VPs inside or outside the page and anything in between, but make sure that here too you try to ghost very carefully and think about the 3d shape of the object. Take all the time you need, remember the 50% rule and when you are ready reply here with your work. Good luck and good work!