Couple of pieces of feedback:

1. There's an order of magnitude difference in the difficulty of problems. Some are hardly more complex than a couple of subscripts and maybe a \frac{}{}, while others need matrix notation. However, they all count as "1 problem." That's pretty weird.

2. There were also a couple of problems where I couldn't figure out why it wasn't accepting my answer, as it was visually identical. It must already be allowing for several variations (\text vs. \operatorname, \over vs. \frac), but Latex is so flexible it doesn't seem to be able to catch all the equivalent ways to solve problems. Plus, there's absolutely no feedback, which means you can sink 30 seconds into a hard problem, not have it accept it, and have no idea what to do next.