Good concept, mediocre balance, poor AI




The ship designer is very fun to use. The problems are that using it is suboptimal - it's most efficient to build almost exclusively empty destroyer hulls - and that the AI either can't or won't use the system, depending on how you frame the question.
Admiral traits only sort of work in that they're all but impossible to gain via experience. Closing off sea zones to shipping also prevents your fleets from entering, which is very frustrating in practice.
Governments in exile and the naval treaty mechanics are modest changes, but they're well-implemented and sometimes impactful.