OK, if you're not bothered about graphics and don't mind the main focus being on naval warfare (ultra realistic units etc.), I'd say you couldn't do better than 'Harpoon 4'.
It's getting on, but that doesn't matter, it's absolutely timeless, and the unit database involved is staggering. The action is strategic and tactical map only with the icons responding to your input.
Best read up a few reviews, because this is hardcore. Completele engrossing, miles ahead of the Total War or Europa Universalis series.
Too involved for today's strategy games.