If you liked Eclipse Eye hiding the sun, you're gonna love many of the other boss intro cutscenes. They really ooze coolness.
As said by the others, the game itself is great, but the PS1 version has way too much slowdown.
I agree that multipliers on enemies destroyed by the options is a bit dumb, but those on enemies destroyed by the laser make sense IMO. In any case, as there are no score-based extends feel free to ignore the scoring if you are playing for the clear and to enjoy the cool boss battles.
If your computer is powerful enough for PS2 emulation, there is a guide
here to play it with various emulator-based graphical improvements (scroll down the page to see example screenshots), though it is far from mandatory to enjoy G-Darius.