A shoot-em-up with a curious pedigree, Metal Black's official subtitle is 'Project Gun Frontier 2', which pegs it as a sequel of sorts to the original Gun Frontier, yet the game's strange, surreal, alien atmosphere, penchant for biomechanical enemy designs, and clear visual cues put it closer to Taito stablemate series Darius than to its predecessor. It has been conjectured that Metal Black was originally intended to be the third game in the Darius series, but was repurposed and relabeled, with Darius Gaiden later going on to take that spot.
Metal Black is notable for being the originator of the "beam duel" concept later used in G Darius, Border Down, and Darius Burst: Chronicle Saviors, where players and bosses engage in what can best be described as "superweapon tug of war", with the loser of the duel sustaining massive damage. In Metal Black this superweapon is leveled up by collecting what the game dubs "Newalone" particles (which bear a striking visual resemblance to the structure of real-life ATP molecules). Collecting Newalone serves the dual purpose of leveling up the player's regular weapon as well as leveling up the superweapon. However expending the superweapon unavoidably drains the regular weapon level down to its weakest point as well, creating an interesting tradeoff mechanic.
The soundtrack comes courtesy of Zuntata, Taito's in-house musical group at the time, and is generally well-regarded, eschewing the genre's traditional pumped-up beats and electronica for moody and atmospheric compositions.
Metal Black was released in Japanese arcades in 1991, and later ported to the Sega Saturn in 1996 by Ving. The Saturn port is considered to be virtually arcade perfect. The game was not brought to Western audiences or ported to any other console until 2006, when it was included in the Taito Legends 2 compilation for PS2, Xbox, and PC. This version is sightly less accurate than the arcade or Saturn versions, as it has a small bug: Normally when firing the superweapon, tapping the appropriate button rather than holding it results in a spread attack rather than a focused beam, providing a small degree of control over the superweapon's area of attack. However in the Taito Legends 2 version, the superweapon alternates between spread and beam modes randomly, regardless of how the button is pressed. For casual players this is unlikely to be a significant concern, and the port is otherwise the same as the arcade and Saturn versions.
Hiroyuki Maruyama of G.Rev has stated that Metal Black is one of his personal favorite shooters, and was a strong influence on G.Rev's Dreamcast shooter Border Down, to the point where he considers Border Down to be a spiritual sequel to Metal Black.