This is a rather slim offering from Nintendo. There are a few game modes: campaign, time trial, periscope shoot and a version of battleships. But the meat of it (the campaign) is rather short--you only have 7 missions to go through, increasing in difficulty, 3 submarines to do it with (a maneuverable one that's low on fire power, a balanced one, and a clumsy one that's got plenty torpedoes). There are rewards for beating the ghosts of the developers--you get a medal, but there's no benefit to doing so (and the medal doesn't even show in your records!); you can collect decals that boost stats of the subs, but I've reached the last mission and haven't been able to collect enough of the cool ones to make a difference. Maybe I'm wrong and there's something in the campaign past the 7th mission. But I wouldn't hold my breath.
It would have been nice if there was a more fleshed out story, some over-the-top nonsense a la Advance Wars: Dual Strike
; this could have/should have been a downloadable title, and most annoyingly, the 3d here is underwhelming.
But it is pretty cool to seat in an office chair and use your 3ds as a periscope. In retrospect, I wouldn't pay more than $15 for this title.