With the popularity of cloud computing services and the endorsement from the video game industry, cloud gaming services have emerged promisingly. In a cloud gaming service, the contents of games can be delivered to the clients through either video streaming or file streaming. Due to the strict constraint on the end-to-end latency for real-time interaction in a game, there are still challenges in designing a successful cloud gaming system, which needs to deliver satisfying quality of experience to the customers. In this paper, the methodology for subjective and objective evaluation as well as the analysis of cloud gaming services was developed. The methodology is based on a nonintrusive approach, and therefore, it can be used on different kinds of cloud gaming systems. There are challenges in such objective measurements of important QoS factors, due to the fact that most of the commercial cloud gaming systems are proprietary and closed. In addition, satisfactory QoE is one of the crucial ingredients in the success of cloud gaming services. By combining subjective and objective evaluation results, cloud gaming system developers can infer possible results of QoE levels based on the measured QoS factors. It can also be used in an expert system for choosing the list of games that customers can appreciate at a given environment, as well as for deciding the upper bound of the number of users in a system.