Well done on finishing a whopping 250 boxes, it's no small feat. I'll be going through the boxes 50 by 50, see if I can give you some solid feedback and see if there was progression while at it. I took a sneak peak at box 250, and I'm pretty sure I'm gonna mark this lesson as complete by the end :)

Boxes 1-50

I had to search for a while, imgur messed up the order of the boxes.

It's a decently good start. Your linework is straight and solid, you're adding lineweights to the outside of the boxes, you are hatching your boxes properly and even the hatching is evenly spaced and you put effort and care into it.

Kudos for all that!

The perspective is still quite messy. I'm sure you have the theory correct, all four lines have to converge in a single spot. When the VP is close to the box, you're doing this wonderfully well, but when the VP is at a distance I see your lines diverging in all kinds of directions.

There are also some boxes, such as 31, where you have drawn over a previous line in what I assume is an attempt to fix a mistake. Avoid doing that! We're drawing 250 boxes after all, if you make a mistake at any one box, live with the mistake and move on. Don't ever try to fix a mark by drawing over it :)

Boxes 51-100

I see you making a lot of sets of 3 lines converging properly, and one suddenly shooting in a different direction. What might help is to realize that the two "middle" of the four converging lines will very often be going in the same direction, almost parallel even.

There's also a few boxes you forgot to extend. 79 and 97, for instance.

Boxes 101-150

Ha, I see you decided that you no longer wanted to waste paper. Generally its recommended to draw your boxes big, it will help your drawing skills a lot more than to draw a large amount of small cubes.

Having that said, the quality of your cubes did improve. There's still a weird few boxes you failed to extend (137, 144), but otherwise most of the boxes you draw actually have proper converging lines!

Boxes 151-200

Good job on experimenting with VPs! You have shallow and dramatic foreshortening mixed all together, and I'm seeing a good amount of creativity in your angles. I am lacking in creativity with your box shapes though, when you are adding boxes to your warmup pool, definitely do consider trying to draw some pizza boxes next time, or some long thin poles or sticks.

Pay attention to boxes like 196, where two of your lines are converging "in pairs", so to speak. I can tell you have the theory right, so mistakes like this don't have to happen if you are careful enough with your planning.

Every page has a box that isn't extended now. It's almost like an easter egg :p

Boxes 201-250

I have very few remarks left. I see variance in box sizes, angles, foreshortening, your lines are (generally) converging properly. You have been adding lineweight all the way, and your hatching is solid. Especially box 249 was really well done!

Overall

Very well done. Your progress over the 250 boxes has been remarkable, and I'm gonna let you move on without asking you for additional boxes. The important takeaway from this lesson is that all the four lines converge to a single point, and I think you understood that well. Your diligence in lineweight and hatching has paid off and is showing itself in the smooth straight lines you are able to draw.

If anything, I would recommend you to take a little bit more time in the planning phase of such boxes. Lines going in the wrong direction like 246, 248, 250 don't have to happen. But then again, you've drawn really strong boxes like 247 and 249 as well. Keep those up and you're gonna draw amazing things :)