A fairly large video download, but an educational watch indeed. The SHMUP documentary
is professionally done, charting the history of STGs from the Space Invaders era up to the latest danmaku offerings from CAVE.
Subtitles are a must. Thankfully detailed instructions are available on how to acquire the free VLC player and use it together with the translation file. There are a few hints on honing your bullet dodging skills as well.