Steel Diver 64.
http://www.nintendoworldreport.com/impressions/36590
Steel Diver: Sub Wars is the follow-up to the 3DS launch title Steel Diver. While the original game was an interesting 2D arcade-like affair that faithfully portrayed the slow, deliberate nature of submarine combat, Sub Wars takes those mechanics and puts them in the 3D first-person space alongside online multiplayer.
While I enjoyed the combat and experience of playing the original, I always felt that the five hours of content failed to justify the then-full price. Nintendo seems to agree, as Sub Wars takes on an interesting free-to-play model. You can only download the eShop version for free on the store itself, and should you choose to go Premium, you do so in-game while Peppy Hare (or someone who looks a lot like him) tries to sell you on it in a way reminiscent of the recent StreetPass games. In Premium, you gain access to seven single-player missions and tons of submarines and crew members. In the free version, you get the first two single-player missions, two submarines, and the full multiplayer experience (which also comes in the Premium version, of course).

As for the game itself, it takes some getting used to (there is a tutorial though, thankfully). As opposed to the linear single-player missions of Steel Diver, Sub Wars is open in a manner not unlike the arena fights in Star Fox 64 (or like most of Command). You use the touch screen to control your depth and submarine speed, change direction, hide your submarine, and launch torpedoes. With its transition to first person, sonar becomes your best friend, as it allows you to to know where other submarines are within close range. Watch out, though -- sonar can't track any subs when they're standing still. The game also allows you to communicate in actual Morse code in multiplayer with the Y button. Once you get the hang of it, it's surprisingly fun. The periscope, which was used in the previous game for a silly mini-game, is now used to look around in all directions.
The best way to describe how combat feels is, surprisingly, exactly what happens when the gameplay of Steel Diver transitions into 3D. It's still deliberate and slow without being boring, and once you learn the ropes, it manages to play like a Star Fox game that relies on stealth while being much more strategic. The way Iwata described it in the Nintendo Direct is as a "contemplative first-person shooter," and that sounds about right. Like other first-person shooters, positioning, staying one step ahead, and fighting smart are the keys to success. Unlike something like, say, Call of Duty, brute force will get you nowhere. The way to play Sub Wars is to play smart or not play at all. Although there is a learning curve that doesn't offer immediate gratification, I found myself having fun after I learned how to play in the first half-hour. Obtaining a certain number of medals unlocks additional submarines with improved stats and room for crew members (who also affect overall stats).
As for content, there isn't a ton to say. The preliminary two missions consist of going through rings and sinking a handful of basic ships, and there are still three difficulties and medal opportunities to enjoy. The multiplayer, for the one match I played, was pretty fun and ran with no complaints. I should warn you to be aware of what team you're on, as I accidentally took down one of my own submarines and lost the game before I realized that the red team is not automatically my adversary.
Steel Diver: Sub Wars seems all right. It plays like Steel Diver pushed into a 3D space, and although that might not work for some, its strategic gameplay and more accessible price point is OK to me.