Intelligent radio access networks (RANs) have been seen as a promising paradigm aiming to better satisfy diverse application demands and support various service scenarios. In this paper, a comprehensive survey of recent advances in intelligent RANs is conducted. First, the efforts made by standard organizations and vendors are summarized, and several intelligent RAN architectures proposed by the academic community are presented, such as intent-driven RAN and network with enhanced data analytic. Then, several enabling techniques are introduced which include AI-driven network slicing, intent perception, intelligent operation and maintenance, AI-based cloud-edge collaborative networking, and intelligent multi-dimensional resource allocation. Furthermore, the recent progress achieved in developing experimental platforms is described. Finally, given the extensiveness of the research area, several promising future directions are outlined, in terms of standard open data sets, enabling AI with a computing power network, realization of edge intelligence, and software-defined intelligent satellite-terrestrial integrated network.