I like the concept and execution. Though as a finished product, some things are left for you to sort out. There are many key bindings left undone and documentation is not extensive. You have to roll your sleeves up and set the bindings yourself in .stumpwmrc config file.
MPlayer crashes if you play a movie. I googled and discovered this was down to the way MPlayer defaults aspect ratio which, if not defined, results in a divide by zero error in CLISP.
I guess if you bypass default and pass an aspect ratio to MPlayer, that should get around the problem. I haven't tried this since stumpwm crashed last night I fired up and used XFCE4. I will try later and post an update.
To pass MPlayer an aspect ratio, do:
mplayer -aspect 2.4:1 nameofmovie.mpg
Here's the page I found describing the error.
MPlayer refuses to run under StumpWM
It looks like the developers are on the case and a fix may appear soon.