I actually think the crew management and interface is a huge leap over SH3.
No more having to drag the bugged guys stuck in the electric room back to diesels when surfacing. No more having to stop TC and check crew fatigue and micromanage that mess.
As for interface, I couldn't stand having to click on some dude's picture and then click on a button above him, and then yet
another button in a list that pops up over that. One click on a symbol and the commands are right below. Although a couple are missing atm.
The TDC is great now that I can input all the manual inputs all while looking through the scope. No more switching to the attack screen and back all the time.