There weren't a lot of scrolling 2D shooters in the late 80s and early 90s on DOS computers because the fundamental differences in hardware between computers and consoles didn't make smooth scrolling an easy thing to do. Heck, figuring out how to accomplish this was a major part of what drove the formation of Id Software when they made Commander Keen. This game is a good example of why smooth scrolling was such a big deal, because this came out in 1993 yet still used a reduced framerate and large scrolling jumps to give the impression of faster-paced gameplay.