Welcome aboard! If you like 688(I), you will enjoy Sub Command. And don't overlook Sonalyst's best selling modern naval game: Fleet Command. You can get Sub Command and Fleet Command (along with 688) as part of the Naval Combat Pack. If you order online, please
have a look at the Subsim Store here, the prices are great and your purchase supports Subsim. Dangweous Waters sells for $15 and the Naval Combat Pack sells for $20: that's three games, all patched and made Vista compatible (trust me, that's important).
I loaded Fleet Command back up last week and have been enjoying the campaign immensley. I'm engaged with the Chinese crossing the Taiwan strait, trying to take out that pesky aitrfiled that keeps launching Badgers and Flankers at my fleet!