mpv is essentially the same video player. It’s based on code from MPlayer and mplayer2, so it behaves more or less like you expect. That means it plays almost everything you throw at it thanks to the ffmpeg libraries, it starts instantly (sorry, VLC, I’ll still recommend you to friends and family!) and the command line options look familiar, even if they have been changed into more standard forms.
Deeper changes include major codebase cleanups, a high quality OpenGL video output driver with higher-precision color transformations, a reworked build system and using system libraries instead of including them in the program source code.
For someone like me who builds all the multimedia toolchain from sources, it’s an advantage. When ffmpeg releases a new version I build that first, and I don’t have to download a second copy and build it again while building MPlayer. mpv uses what’s available. It’s the same for libass or x264, the latter being an example of external library not included when you download the MPlayer source.
This results in much faster compilation times and a much improved situation for packagers, in my humble opinion.
The icing that tops the cake are periodic releases, so you know exactly when you should upgrade as developers mark interesting points in the project history.
And the only drawback is the surprising muscle memory. After more than 10 years typing “mplayer” and with “mpv” sharing a common two-letter prefix, it’s amazing how most times I have to focus a lot to type “mpv” correctly.