Generating human-like robot motions is pivotal for achieving smooth human-robot interactions. Such motions contribute to better predictions of robot motions by humans, thus leading to more intuitive interaction and increased acceptability. Human likeness in robot motions has been conventionally measured and realized via the optimization of human-likeness metrics. However, the abundance of such metrics and the absence of standardized criteria impede their usage in novel contexts. In this work, we introduce a unified human-likeness metric built from a hierarchically weighted sum of individual metrics. The proposed metric is derived from a thorough analysis of eleven existing human-likeness criteria and is applicable across various tasks and robot models. We evaluate its performance in the context of motion retargeting of bimanual tasks with three different humanoid robots.