I'd thought VLC had dropped support for MIDI, but I've found it to be the easiest way to get hassle-free MIDI playback.

1. Install VLC as usual
2. Install vlc-plugin-fluidsynth
3. Install a soundfont
4. Point VLC to that soundfont via Tools > Preferences > Input/Codecs > Audio codecs > FluidSynth

Now you can play a MIDI file just like it's any other audio or video file :)

• MIDI