For the first 50, while the quality of your lines is generally smooth, I notice some instances of arcing, like in box 10, box 33 . I also saw a few points where it looked like a line was redrawn multiple times, like box 20 and box 34. I also noticed lines pair off and converge towards two vanishing points, such as box 15's red lines, box 28's red lines, and box 46's red lines.

For the next 50, while your lines show improvement throughout this set, I noticed some more instances of arcing, like in box 70 and box 92. I see improvement in your convergences as well, though there are a few more instances of lines pairing off, like box 60's green lines and box 82's green lines.

For the last 150, there is continued improvement in your lines, though there are a few more instances of arcing, like in box 122, box 150, box 175. That said, I noticed fewer of them towards the end of the set.

I also see further improvement in your convergences. However, there are more instances of lines pairing off, like box 108's red lines, box 157's green lines, box 186's red lines, and box 233's green lines. In these boxes, the inner lines (green and orange in this diagram) diverge instead of converging at the vanishing point. Keeping in mind the angles of neighboring lines can help when planning the box's construction.

As an aside, some of your boxes get a bit small on the pages, like box 55, box 86, box 95, box 117, and box 195. Drawing larger boxes is more effective for practice, as it'll help you engage your whole arm from the shoulder, and will engage more of the part of your brain that processes spatial reasoning.

All said, I'm going to mark this challenge as complete.