I think AM and WW both make a good basis for a solo game. With AM you have the chance for multiple environments, Atlantis, the open water, deep sea trenches, towns and cities on the shoreline, vessels at sea, submarines, reefs and so forth. You can go on quests, help out NPCs, deal with threats ranging from accidents like a sinking ship to an oil spill to stopping monsters from the deep or rebel Atlanteans from attacking the surface world. There's lots of phases to Arthur's life as well. You could have levels where you learn his powers when he's a kid or teenager, his time alone after his father died, being imprisoned by the Atlanteans on a chain gang, freeing Atlantis from tyranny and then ascending the throne. It's all there waiting to be adapted.
