Current clinical methods for the assessment of Parkinson's disease (PD) suffer from inconvenience, infrequency, and subjectivity. WiiPD is an approach for the objective home-based assessment of PD which utilizes the intuitive and sensor-rich Nintendo Wii remote. Combined with an electronic patient diary, a suite of minigames, a metric analyzer, and a visualization engine, we propose that this system can complement existing clinical practice by providing objective metrics gathered frequently over extended periods of time. In this paper, we detail the approach and introduce a series of metrics deemed capable of quantifying the severity of tremor and bradykinesia in those with PD. The system has been tested on a 71-year-old participant with PD over a period of 15 days, a 72-year-old control user without PD, and a group of eight young adults. Results indicate a clear correlation between patient self-rating scores of tremor severity and metric values obtained, in addition to clear differences in metrics obtained from each user group. These results suggest that this approach is capable of indicating the presence and severity of the motor symptoms of PD that affect arm motor control.