The Saturn's Stunner has always been my favorite light-gun made for the home, so I may be slightly biased pro-Saturn light gun games. The Namco gun for the PS is slightly more accurate, but nothing beats the spring-action on the Saturn's Stunner. That being said, A51 for the Saturn basically rocks.
There's an annoying border around the screen, and things are a slight bit pixelly. Also, you must shoot an icon on the border to enact the grenade, since there's no button on the gun for this. But those are the only complaints one could have, and this is a fantastic arcade translation. The pacing, sound, and well designed shots keep this game in good company as shooters go. About as arcade perfect as you could hope for, and a riot.