Tenzou, the protagonist is a student who is accidentally shot by an apprentice angel Patoko, with a Cupid Arrow. The blessing from the arrow makes Tenzou irresistible to the opposite sex, transforming him into the most popular boy in school for one day.
The catch is if Tenzou is unable to find his true love before the effects of the Cupid Arrow wear off, he’ll be destined for a life of loneliness.
Originally only for the Xbox 360, a PS3 port with additional characters and PlayStation Move support has been released on February 23, 2012.
Gal Gun plays is basically a rail shooter, with the player walking through the school - As girl after girl runs towards the player trying to profess their love via hand-written notes or screams. Armed with "pheromone shots", the player keep the girls at bay by shooting and dropping them to the floor in dizzy ecstasy - All the while trying to cultivate a romance with one of the four main female leads.
The shooting is broken up by "action events" - Similar to that of a boss battle as well as a doki doki mode ("anxious" or "excited" in English) where the player has the option to zoom in and stare at one particular girl he fancied.
The developer has also added a panic button that switches the action for a retro-looking game, with authentic animations and sounds. This is referred to as a Mama kita gamen or "Mom arrived screen,".
Source: Wikipedia, "Gal*Gun", available under the CC-BY-SA License.