[en] We systematically studied the electronic structures of two-dimensional (2D) multilayered nickel bis(dithiolene) sheets using first-principles calculations. The monolayer is semiconducting, while all multilayers become good metals. We reveal that the metallicity mainly arises from covalent-like interlayer interaction between the 3p _z orbitals of S atoms in adjacent layers. We show that such interlayer orbital hybridization widely exists in many 2D layered materials involving extensively out-of-plane orbitals. This interlayer orbital hybridization greatly enriches the physical properties of this class of 2D layered materials compared to pure van der Waals 2D layered materials. More importantly, we demonstrate that these properties are easily tunable by controlling the interlayer distance or stacking, making them very promising in meeting the desired requirements in practical applications. (paper)