In before Elixir.
The worst shooter I've ever played is Ibara for PS2. Battle Garegga was such an amazing and fun game, and then they have to turn around and make an animu bullshit sequel which looks terrible in yoko and is only playable in tate.
I mean, I wouldn't mind Ibara if the bullets were actually visible and you weren't guaranteed to die on bosses if you didn't have any full bombs. Seriously some of the bullets in Ibara are so transparent I'm surprised they even managed to get through testing.
Runner up is Mars Matrix, which I just plain don't like.
The best I've played is probably Dodonpachi Daioujou or Ikaruga. Daioujou is a game that still looks amazing, puts you on the edge of your seat after years of playing it, and the exact same thing could be said of Ikaruga. I haven't single credited these games and probably never will (only Mushi and Dodonpachi so far) but I really enjoy their style.
How ya doing, buddy?