Why the game hasn't been announced for Virtual Console yet: This is one of the best and best-known TG16 games, and IREM has already proven amenable to having their games available on the Virtual Console, so we can count on seeing Ninja Spirit soon. We just wanted to talk about it.
Why we think it should be on the Virtual Console: The fact that Ninja Spirit was very popular for a TG16 game still doesn't mean that a lot of people played it. Luckily, the Virtual Console can heal the wounds from the 16-bit console war, of which the TG16 was the first casualty.
Ninja Spirit doesn't really cover novel territory-- as a vengeful ninja, you run, jump and slash demons with a sword, you throw shuriken and bombs, and you spend a lot of time in dark forests (the natural habitat of the ninja). But it doesn't matter that the subject is familiar, because every aspect of Ninja Spirit is perfectly designed. The graphics are colorful and clear, and the difficulty, while severe, is not as brutal as that of many action games. Where The Legend of Kage was full of unavoidable one-hit deaths in mid-jump, Ninja Spirit mitigates the issue with a lifebar. In another nice touch, you are given all four of your weapons upfront, and are free to choose between them. You can then upgrade them with powerups.
The graphics, the difficulty, and the weapon selection aside, the most important thing about Ninja Spirit is the control. It doesn't even matter if you never pass the first stage; replaying the first stage over and over again is so much fun because it is so much fun to run around, jump and slash in this game. The joy of just moving your ninja around is amplified once you've got your ninja shadow clone guys (as in Ninja Gaiden 2).
We love all of the games we've profiled in Virtually Overlooked, but this is the first one we can recommend to everyone with absolute certainty. When this is released, buy it. It is an objectively excellent game.