I own both the earlier titles and have just acquired this one. Having played it through once I would say that the games are essentially the same, but with some minor differences.
The most noticeable is the differentiation between 'Convoys' and 'Battles'. In the former, players go through one round in the manner you would recognise from the earlier games. With the latter, two rounds are always fought, with the cards in the second round being played face down. The basic rules require a player to stay true to his faction in the second round of play here, but the optional rules allow you to switch sides. The rule book is not clear on how the 'fate' mechanism is affected by the face down card play. My group wasn't sure whether to determine results after all cards were revealed, or just treat fate as 'suspended' for the face down cards.
There are more neutral special effect cards which are generically known as 'Storm' cards. Some represent bad weather, but others intensify air attack capability or prevent submarines from operating (the 'Shallows' card).
One thing I did notice is that while the time-honoured Ultra and B-dienst cards are present, the Pacific Typhoon approach of having the intel cards 'fated' against each other is not applied in this game.
Overall, despite some niggles about an image on the cards and some historical text inaccuracies this strikes me as a really good game and well worth getting. More so if you enjoyed Atlantic Storm and Pacific Typhoon.
Humble apologies - further to my last I re-read the rules and found I had missed a bit about the fate mechanism in Battles. It does apply to face down cards played in round two, and the effects are applied "as players become aware of them" when the cards are revealed.
The minor historical niggles were that one British destroyer card is represented by a photograph of HMS Hood (!), HMS Eagle is described as a merchant aircraft carrier, and HMS Illustrious as an escort carrier. I'd remarked in the comments section that the Axis must have hated to meet our fleet carriers!