With the recent technological evolutions in networks and increased deployment of multi-tier clouds, cloud gaming (CG) is gaining renewed interest and is expected to become a major Internet service in the upcoming years. Many companies have launched powerful platforms such as Google Stadia, Nvidia GeForce Now, Microsoft xCloud, Sony PlayStation Now, among others, to attract players. However, for all endusers to fully enjoy their gaming sessions over the wide range of network access qualities, CG platforms must adapt their traffic. In this paper, we present the outcomes of a comprehensive measurement study performed on the four aforementioned CG platforms, configuring different synthetic network constraints like packet loss, throughput decrease, latency increase and jitter variation to observe the traffic of these CG platforms under degraded network conditions and infer their adaptive behaviour. We also present how the four CG platforms behave when used under real cellular network conditions, captured on the Orange network in January 2022. Our findings show that the four platforms exhibit different adaptation behaviours. Moreover, many cases result in a degraded QoS, leaving room for further improvements at both application and/or network levels.