a) A game engine that fully supports multiplay in both submarine and surface escort roll...meaning Destroyer Command ( insert number here ).
b) multiposition multiplay submarines...players can get together and each take on a role within the same submarine. Skipper, engineer, watch officer, sonar/radar operator, lookout, gunner etc.
c) Authentic weather generation...no more of SH3's calm one minute / perfect storm the next.
d) Pacific ambience...meaning fabulous sunsets, tropical night skies ablaze with stars with the dark shapes of islands slipping past ( maybe with the occasional cooking fire glowing on the beach )... believe me, I've sailed those seas and I know what its like!
e) More detailed damage/breakdown models. You're sailing along one day off Formosa, and you're informed that an evaporator has broken down. What's an evaportaor, you might ask ? What impact will it have on the boat's ability to stay on patrol ? Does my engineer officer have enough skill points ( awardable between patrols ) to fix it ?
f) the ability to name your own boat.
I'm sure I'll think of some more