Going to give a plug to the recently-released REVOLVER360 RE:ACTOR
on Steam that's 30% off (7USD) for its debut, and it's DRM-Free and comes with the soundtrack. If you like bullet hell-ish shoot-em-ups this is in league with the best of them - it's been around in Japan for nearly a year now.
Personally though I'd recommend supporting the publisher (which localized it) directly and buying it there for the same price
, as you get both a steam key and a extra DRM-Free copy (that skips Steam entirely, if you dislike Steam that much).
Like most shoot-em-ups you'll probably want a controller.
Sidenote: This isn't on GOG... why?!?!?