Sidescrolling shooting games aren't as popular now as they once were. Back in the days of the NES (and early SNES too) these sort of games were all the rage. Tubular Worlds is a pretty good space shooting game, where the screen scrolls left and you shoot wave after wave of enemies while collecting powerups for your ship. Nice graphics and SB sounds/music. (Note: It ran a bit choppy on my system, I assume that this was probably due to an incompatibility with my hardware.)