The long-term Generation Expansion Planning (GEP) problem determines the optimal type of energy technologies, size, location, and time construction of new power generation plants, while minimizing total cost over a long planning horizon and being subject to a series of constraints. Due to its complex nature, its effective implementation requires the consideration of a wide range of aspects including economic, environmental, regulatory, technical, operational, social, as well as potential interdependencies with other complementary sectors. As a consequence, the traditional cost-based approaches have been extensively modified and updated, leading to more advanced ones including, at least partially, some of the above described aspects. This work provides a comprehensive review of the most recently developed approaches dealing with the Generation Expansion Planning problem from a variety of perspectives, organizing them into seven key categories including the interaction of generation expansion planning with: the transmission expansion planning, natural gas system, short-term operation of power markets, electric vehicles, demand-side management and storage, risk-based decision making, as well as with applied energy policy including security of supply. The main goal of this work is to stress the multi-dimensionality of the generation expansion planning execution, creating the need for an in-depth investigation and consideration of synergies with other complementary sectors. Reviewing results have the objective of providing useful insights into the current state and future challenges of the GEP decision-making.