I just want to clear up one thing because I'm a stickler for this sort of stuff. Mahjong, as the West knows it, is actually Mahjong Solitaire, also known as Taipei. The actual game of Mahjong is a three-to-four-player tile game similar to poker in execution. It's fun! Check it out.
Anyway, Mahjong Cub3d is the first three-dimensional variant of Mahjong, available on the 3DS. In this game, you must match pairs of tiles together to clear a board. Since there are rules to which tiles can actually be selected (can't be covered by another tile, can't be surrounded by tiles), it is possible to face an unwinnable board, and this is where the strategy comes from.
3D Mahjong isn't much different from its 2D counterpart, only now instead of looking down at a stack of tiles, you're staring at a bunched-together object consisting of tiles, forcing you to rotate the board to find different angles and tiles to match. Tile selection is done by moving the analog stick, which is a bit of an odd choice I would've preferred the stylus instead but it works well regardless.
There's a lot here to play through, if you like Mahjong. The number of boards never seem to end, and there are even multiple difficulties to play through on each. You're timed, which can be a little stressful in a game which I would assume is supposed to be relaxing, but you're also given hints if you get stuck, so it tends not to be a problem.
There's also a 2D-mode of play, if classic mahjong is more your thing, but it's not very well done. The camera is set at such an angle that makes it hard to tell which tiles are on what level, so it's a bit of an exercise in frustration trying to find what can be matched.
That's really all there is to say about the game. For what it is, it's done well. Mahjong Cub3d successfully brings mahjong (solitaire) to the third dimension, and if you like the original, then I don't see why you wouldn't like this.