Mixed reality (MR) has emerged as a promising tool for rehabilitation, offering immersive and interactive experiences that enhance patient engagement and increase motivation, without detaching them from their reality. This paper presents some preliminary usability and feasibility results about MiRR (Mixed Reality Rehabilitation), a prototype MR application developed for cognitive and motor rehabilitation using Microsoft HoloLens 2. The system integrates spatial computing, hand tracking, and real-time feedback to create engaging rehabilitation exercises that could be tailored to individual patient needs. MiRR was designed to stimulate patients by presenting tasks aimed at improving motor coordination, spatial awareness, and cognitive functions. The application provides guided exercises that require patients to interact with virtual objects with their hands or stepping onto virtual tiles placed on the floor. The MR device would also continuously collect measures during the exercises, allowing clinicians to track patient progress more objectively. This preliminary study was conducted with a small group of healthy subjects and rehabilitation specialists of Fondazione Don Carlo Gnocchi, to foster feasibility, usability, engagement, and potential therapeutic benefits. The qualitative feedback gathered suggests that MiRR may enhance motivation, improve adherence to rehabilitation protocols, and provide valuable data for clinicians to personalize therapy plans. Further and larger studies are needed to assess the efficacy of this MR-based treatment, and to thoroughly investigate the measurements and the derived indexes for an objective evaluation of the subject’s performance. Despite the obvious limitations and the early stage of development, it seems that MiRR, leveraging the interesting features of MR technology, may contribute to developing novel, engaging, flexible, more personalized, forms of rehabilitation.