This game isn't particularly obscure, being a first-party Sega release in one of its major (at the time) franchises. But it doesn't matter, because this game is also the most awesome release in that franchise. Shadow Dancer: The Secret of Shinobi answers the question of what could possibly be cooler than a ninja stalking around a gritty urban landscape: that ninja's dog. Seriously, you'd have to be a pretty cool dog to keep up with Joe Musashi (or his son, depending on the region).
This game violates an implicit Virtually Overlooked rule by having been released on the Virtual Console in Japan. This happened way back in December of 2006, so we actually feel more than justified in whining about its current unavailability outside of Japan on the Virtual Console. It would be incredibly easy to release it, since it's already been released on the Virtual Console, and Sega just refuses to get around to it.
Shadow Dancer plays much like its predecessor, except that Joe can only sustain two hits at most and has unlimited shuriken. There is also more of an emphasis on two-tiered design; by pressing up and jump, Joe can jump to a higher platform or, in some cases, deeper into the stage (behind a fence in one memorable example). The goal of the game is to rescue hostages throughout the level, much like another famous Sega sidescroller of the time. There's also an enjoyable bonus level in which Joe jumps off the side of a building and throws shuriken at other ninjas as they climb up. It's like Galaga in reverse, with crazy people.