Way to power through the 250 boxes! Overall, they look good. You have confident lines that converge pretty well through the whole set.

One thing I'll note that's not a mistake per se, but rather a tendency, is that many of your boxes have convergences that are very close to the box. That is, they're dramatically foreshortened. This applies most often when your object is either very close to you, or very large. A few of your boxes have more subtle convergences where the lines would meet "off page," like box 145. This applies when your object is smaller, or farther away.

My question is, do you have a feel for how to control convergence--whether it's dramatic or not? If you feel like the amount of convergence you put in is intentional, then that's just fine. If it feels more unintentional, or you are less confident in making "subtly foreshortened" boxes, then you may want to try 10 or so boxes where the lines would converge off page. (Use this as a warm up exercise a few times.) You could even try a few with a ruler and a second attached page at first, to see what angles work best. (I hate to say "hey, draw more boxes" when you've just finished 250, but when you recover a bit, this might be good to do in a warm up at some point. Again though, you have a better feeling for whether you might need to try this or not.)

Other than that, nice work, and congrats on getting through that beast of a challenge!