I've got four major issues with SC that I'd like to get comments on:
1. Maybe just my own ignorance, but is it possible to conduct real amphibious assaults? i.e. assault an enemy unit directly from a transport? If this isn't allowed for I can see major opportunities for exploitation (line the coast with a wall of corps). Specifically I've found that Malta is nearly impossible to capture because of the strength of the defending air unit and the fact that you can't land any ground troops. Admittedly, allowing for real amphibious assaults is difficult since there's no automatic retreat in the game, which brings me to point 2:
2. Allow for units to automatically retreat when too much damage is done to them (say if they suffer >30% casualties from the start of the turn while on defense they retreat). Without retreat built in we can't have amphibious assaults and it creates some unrealistic situations in general.
3. Stacking. I can understand no stacking for Armies, but you should be able to stack multiple planes/ships, maybe even multiple Corps, as well as ground units and planes in the same hex.
4. Sub spotting range and sub ops. Right now subs can be seen from 1000 miles away (literally) and attacked by anything, even battleships which would realistically have no anti-submarine weapons. IMHO reduce sub spotting range to 1 hex (can only be seen from an adjacent hex) and introduce the Destroyer as the only ship type that can attack subs, along with Carriers.