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Abstract Few‐layer transition metal dichalcogenides (TMDs) and their combination as van der Waals heterostructures provide a promising platform for high‐performance optoelectronic devices. However, the ultrathin thickness of TMD flakes limits efficient light trapping and absorption, which triggers the hybrid construction with optical resonant cavities for enhanced light absorption. The optical structure enriched photodetectors can also be wavelength‐ and polarization‐sensitive but require complicated fabrication. Herein, a new‐type TMD‐based photodetector embedded with nanoslits is proposed to enhance light trapping. Taking ReS2 as an example, strong anisotropic Mie‐type optical responses arising from the intrinsic in‐plane anisotropy and nanoslit‐enhanced anisotropy are discovered. Owing to the nanoslit‐enhanced optical resonances and band engineering, excellent photodetection performances are demonstrated with high responsivity of 27 A W−1 and short rise/decay times of 3.7/3.7 ms. More importantly, through controlling the angle between the nanoslit orientation and the polarization direction to excite different resonant modes, polarization‐sensitive photodetectors with anisotropy ratios from 5.9 to 12.6 can be achieved, representing one of the most polarization‐sensitive TMD‐based photodetectors. The depth and orientation of nanoslits are demonstrated crucial for optimizing the anisotropy ratio. The findings bring an effective scheme to construct high‐performance and polarization‐sensitive photodetectors.