I bought this game as I was looking for something a bit different for my 3DS from the usual fare and was pleasantly surprised.
The main bulk of the game sees you piloting one of 3 different types of submarines through some increasingly tricky levels. I found this great fun and very different from anything I've ever played before.
While the controls seem a bit slow and unresponsive at first, after a couple of goes it all starts to make sense and you really get the impression that you are actually piloting a submarine. To progress in the game you really need to plan ahead and its almost a cross between a RTS and a side-scrolling shoot-em-up.
Many reviews are critical of the apparent short length of the game but to complete all the levels on Expert level with all subs is a genuine challenge. And once you've done that there are the medals to win by beating the staff ghosts on each level (very tough!) and bonus decals to collect to improve your subs abilities.
The 3D is the game is pretty well done. Its mainly quite subtle and adds a bit of depth but there are some really cool effects every now and then that really add to the experience.
So if you are looking for something different and like the sound of the game why not give it a try!