In the health domain, the field of rehabilitation suffers from a lack specialized staff while hospital costs only increase. Worse, almost no tools are dedicated to motivate patients or help the personnel to carry out monitoring of therapeutic exercises. This paper demonstrates the high potential that can bring the virtual reality with a platform of serious games for the rehabilitation of the legs involving a head-mounted display and haptic robot devices. We first introduce SG principles, nowadays rehabilitation context, and an original applied haptic device called Lambda Health System. The architecture of the model is then detailed, including communication specifications showing that lag is imperceptible for user. Finally, to improve this prototype, four serious games for rehabilitation using haptic robots and/or HMD were tested by 33 health specialists.