X-Out

In principle, this is yet another (technically very impressive) horizontally scrolling shoot-'em-up. The interesting twist about the scenario is that it doesn't play in space like the similar game R-Type and most of its clones - instead, the fight between good and evil is underwater. Through five levels, you have to shoot countless enemies, complete with the obligatory mid-level and end-level bosses. The most innovative part of this game comes after a level when you get to purchase new weapons - instead of simply buying upgrades, you can customize your ship by placing your new weapons anywhere on it.