Did not played multiplayer yet since i like to play my way, untill i know how to master evrything (or mostly). Got right now 8 hours of singleplayer time. But there are some points that is personally for me necessary to make singleplayer way more addictive.
1) There should be a mode selector for singleplayer that you could choose for character swapping (how it is now) and a mode for sticking up to 1 class. You pick medic, you play medic in the whole campaign mode, you play engineer you stick to engineer (no character swapping) and etc...
2) On this moment you can play with any submarine you want (+ from steam workshop) if it is big or small it doesnt matter. But it would be nice to pick from a several standard submarines as your starter pick. If you want bigger ones, spare creditz and buy bigger submarines (or upgrade them on a base, see point 4). This could be an option, if you want to make your way up to bigger and bigger or not. (example: you start with a bicycle and make your way up to get a bigfoot).
3) Make bots more smarter on some stuff they are uhmm annoying (example's: they cannot control a submarine; fixing leaks more efficient; putting the equipment back where it should be. pretty annoying when you have serious problems and cant find a dive suit
)4) I did not saw it yet but it would be awesome, that you can upgrade/ remove or have changes for your submarine on bases. Lets call them a construction base. Evrything you want to change on your submarine that you can do if you have enough spare credits.
5) Did not encountered yet in singleplayer and i think it is not in the game anyway, that you could encounter friendly and or enemy submarines (maybe this is too much ?).
6) (For me) Its logic when you are docked into a base and your engines are turned off, your oxygen is generated from the base you are docked on. But its not and i almost died
Let me know what you think from these idea's.
If you need more explanation or got better idea's on some of these points dont hesitate to ask ;)
Greetz,
Madrush