The rapid evolution of communication technologies has paved the way for a paradigm shift in network infrastructure, particularly in the context of Non-Terrestrial Networks (NTN). This article offers an in-depth exploration of the remarkable advancements catalyzed by the 3rd Generation Partnership Project (3GPP), notably with the advent of Releases 17 and 18. At the forefront of this transformation is the integration of satellite access networks into terrestrial counterparts, a breakthrough that demands a unified, multi-dimensional design approach. From the fundamental Radio Access Network (RAN) to intricate services and system aspects, extending to core infrastructure and terminal equipment, every facet undergoes profound scrutiny. The article meticulously examines the implications of satellite access network incorporation, both as a newfound 3GPP RAN and as a pivotal backhaul solution. Central to this analysis are the seismic shifts in network architecture and performance metrics, taking into account critical factors such as coverage, capacity, and latency. Delving into the crucible of 3GPP Release 18, the article identifies and addresses key challenges, proffering innovative solutions within the ambit of the NTN framework. These solutions are poised to be instrumental in fortifying the integrated architecture necessary to propel 5G and beyond into the future. This comprehensive analysis serves as a critical compass, guiding stakeholders, technologists, and policymakers through the dynamic terrain of NTN, illuminating the path toward a more interconnected and technologically advanced era of global communications.