A real story's nice, but Aquanaut's Holiday is also a better game for its staggered progression. The atoll's dotted with sonobuoys: oval-shaped capsules left behind by Bill that send out navigation signals. Unfortunately, they've all run out of power, so it's up to you to replace their batteries when you see them near the surface -- doing so opens up new navigable sections of the atoll. And since you can only carry a few batteries at a time, you'll have to go back to the island base and buy more. So, not only do you have a clearly defined point to your exploration, but most of it's kept from you at the start, making your progression and discoveries more rewarding (especially when the camera transitions to a sweep of the area with an epiphanic bagpipe tune accompanying it).