Transshipment is the process of off-loading an intermodal loading unit (for example, different types of containers, semitrailers, swap-bodies, and so on) from one means of transport (for example, a vessel, a freight railcar, etc.) and loading it onto another. Such a process, as well as other logistics services related to loading units, may take place at a transshipment terminal, which is the intermediate node added to an intermodal transport network when combining two or more liner services that facilitate freight transport. Growing customer requirements affect transshipment terminal operations and contribute to the development of comprehensive logistics services. Terminal clients expect the delivery of complex services that often pose serious challenges to terminals providing these services. The specific decision-making tools are essential for facilitating the shaping of terminals’ complex service offerings. In this study, we investigated the issues connected to the complexity of logistics services offered by transshipment terminals. The aim was to develop a decision-making approach to assess the complexity of logistics services offered by these terminals. A procedure for the formulation of complex and comprehensive service sets at transshipment terminals, which includes sustainable energy and energy efficiency issues, was proposed. The approach for assessing the complexity of services at terminals handling intermodal loading units was developed, and an appropriate mathematical model was applied. Consequently, indexes of the efficiency and comprehensiveness levels of ordered services in a terminal were proposed. The ranking of decision-making criteria influencing the shaping of complex service offerings was created based on the results of a questionnaire survey distributed among the managerial representatives of terminals located in Poland. The data obtained with the use of a questionnaire survey allowed us to verify the proposed approach. The research results may be useful for the management of transshipment terminals while making decisions on the creation of comprehensive services offered to their clientele.