MY fave shoot em up was on the PSOne. It was an import of a game called EINHANDER. (dunno if this has seedy German meaning or not)
A brilliant game that sadly for everyone else, never made it over here. (as far as I know)
It was a great 2D game that used 3D backgrounds. Very good looking.
On the Amiga it would have to be Project X, never managed to complete it though
only got as far as the underwater level.