Another of those games that have really slick intros and some nice production values, such as music, but that in the end just aren't all that fun to play.
In fact this one darn near put me to sleep. Granted it was late at night, but surely having long stretches where you can just hold the fire button down without moving isn't all that conducive to a fun play experience.
Since most shooters feel the need for a gimmick of some kind, the gimmick here is that you can select different directions to shoot your laters: forward, backward, up/down, or four-way diagonal. Now, four-way diagonal has four different shots, whereas the others have at most two, sometimes one... So which might you want to use most of the time? Yes, diagonal.
Of course, the game designs levels and bosses such that you can only hit vulnerable spots by switching to a different shot type. This keeps you guessing a bit, I suppose, but it isn't all that thrilling to have to be cycling through your shot types constantly.
Specifically, according to Wikipedia, this PC Engine version was upgraded from the arcade original, "Hellfire": "Hellfire S contained notable differences from the other versions, including a remixed, more orchestral soundtrack, animated cut scenes, and the replacement of the leading male character Lancer with a female character called Kaoru."