Mobile cloud gaming allows gamers to play games on resource-constrained mobile devices, and a measurement study to quality the client performance and energy consumption is crucial to attract and retain the gamers. In this paper, we adopt an open source cloud gaming platform to conduct extensive experiments on real mobile clients. Our experiment results show two major findings that are of interests to researchers, developers, and gamers. First, compared to mobile native games, mobile cloud games save energy by up to 30%. Second, the frame rate, bit rate, and resolution all affect the decoders' resource consumption, while frame rate imposes the highest impact. These findings shed some light on the further enhancements of the emerging mobile cloud gaming platforms.