Astal, known in Japan as Kisuishou Densetsu Asutaru, (輝水晶伝説 アスタル lit. Shining Crystal Legend Astal) is a 2D side scrolling platformer game for the Sega Saturn. Astal was released early in the Sega Saturn's life and used hand-drawn graphics.
At the time of Astal's release, the video game market saw the release of new, increasingly popular genres, and 3D games were in high demand. This factor is a possible cause resulting in Astal's poor sales, despite positive reviews. Also, the North American release has the oddity that the game's title does not appear on the side of the case, which is blank apart from the Sega Saturn logo. This meant that gamers would be unlikely to notice the game on the shelves unless their specific retailer chose to display it with front cover out. Regardless of the reasons behind why Astal sold poorly, the game is now considered a minor rarity.
It should also be noted that Astal never received a PAL release.
Source: Wikipedia, "Astal", available under the CC-BY-SA License.