That's strange - I did not have any difficulty with the exercises and found them to be clearly specified! All the exercise problems were neatly broken down into small functions - you simply had to fill up the body of the functions!
The exercises were not all that difficult (especially given that there were unit tests for almost all of them), but they did have issues. Some of the tests required you to use functions that didn't appear until one or two lectures later.
Most likely the GP is complaining about the fact that the server-side tests were on bigger datasets than the ones that shipped with the code; but that wasn't a big issue as you could keep resubmitting up to the deadline.
I found it useful to remember that almost all of the solution functions were very short; most were one line, some up to five; if you were writing long functions you're most likely doing it wrong. Similarly, the local tests should finish almost instantaneously. If they take 30s with the local dataset, they'll time out with the larger dataset on the server.
