This is purely just mine:
1) Interface - Obviously
2) Aiming system - maybe not a 100% change but certainly a change
Even when NOT using the join up the circles method... ( too easy )
you can just use the map and torpedo path line on the mini map and then fine tune it by altering AOB and bearing to be obviously just right for a hit. ( still too easy ) The only way I can get it to be really hard is by diasabling map contact update..... then its darn near impossible...well to me! lol
3) A. I . without the darstardly destroyers mod enemy ships seem too easy...lol but with that lovely mod ...holy schmitt! not sure I can cope with it! lol
4) The Crew -- for me this must be next because its just ruins the feeling of emersion when I watch my sub dive everytime but the watch crew only go below when they are up their necks and heads in sea water.
And the morale system -- of course.
What do you all think?