Streamlined CLI options
MPlayer's options parser was improved to behave more like other CLI programs, and many option names and semantics were reworked to make them more intuitive and memorable.
On Screen Controller
While mpv has no official GUI, it has a small controller that is triggered by mouse movement.
High quality video output
mpv has an OpenGL based video output that is capable of many features loved by videophiles, such as video scaling with popular high quality algorithms, color management, frame timing, interpolation, HDR, and more.
GPU video decoding
mpv leverages the FFmpeg hwaccel APIs to support VDPAU, VAAPI, DXVA2, VDA and VideoToolbox video decoding acceleration.
A straightforward C API was designed from the ground up to make mpv usable as a library and facilitate easy integration into other applications.
mpv is under active development, focusing on code refactoring and cleanups as well as adding features. Want a feature? Post a patch or request it!