>I'm assuming this is the only 2D shooter for the PSOne, but if anyone
>knows of others (imports or domestic), please let me know.

Too many to mention (a common misbelief by some that the PlayStation was only
about 2D games...these people need to import more often). You can always go
over to Sony's Japanese site to research what shooters came out and when;
however, I'll start you on your path by just listing the 2D shooters (or
collections which contained 2D shooters) which came out for Saturn which also
made their way onto PlayStation (or vice versa):

Bokan To Ippatsu! Doronboo
Capcom Generation 1
Capcom Generation 3
Capcom Generation 4 (yes, Gun-Smoke is a shooter)
Cho Aniki: Kyuukyoku Muteki Ginga Saikyou Otoko
Darius Gaiden
Detana! Twinbee-Yahoo Deluxe Pack
Do Don Pachi
Don Pachi
Geki-Oh Shienryu
Gokujyou Parodius-Da! Deluxe Pack
Gradius Deluxe Pack
Gunbird
Jikkyou Osyaberi Parodius
Kaitei Daisensou
Konami Antiques MSX Collection (volumes on the PSX, one collection on SS)
RayStorm (Layer Section II on SS)
Salamander Deluxe Pack Plus
Sexy Parodius
Sol Divide
Sonic Wings Special
Soukyugurentai
Strikers 1945
Strikers 1945 II
Super Dimension Fortress Macross
Thunder Force V

Um...the only one I'm not certain if it came out on PlayStation, though, is
Space Invaders. Taito released it for Saturn; I have it. Still, that's just
Space Invaders. In my opinion, though, the best 2D shooter for PlayStation
(and exclusive to it) is Konami's Gradius Gaiden...so I'd recommend that
(yes, I like it better than Zanac X Zanac). Additionally, I'd also suggest
picking up the import Dezaemon Kids, which has a bonus disk which contains
102 or so sample shooters made with the software, many of which will remind
you of PC Engine games. While certainly lacking on the domestic side with a
rather spartan release of shooters in comparison to what came out in Japan,
Sony did bring over Seibu Kaihatsu's Raiden Project...which contains an
utterly fantastic rev of Raiden II.

- Grant