Editors' Note, March 13, 2014: This review was updated to include impressions of the Android version of Threes.
Threes (Android|iOS) is a part-math, part-matching game as you slide numbers to make multiples of three while trying to get the highest score possible. At first blush, it doesn't seem very exciting, but once you hear the music and sound effects, and get into the flow of the game, it can be incredibly addictive.
What's amazing about Threes is that it came out only one day before this review, but it's currently sitting at No. 1 in the paid app listings at the App Store. It's taking it a bit longer to reach the top of the charts on Android, but we think it could easily catch up soon. Once you start playing and get to know the game, you'll quickly see why it's so popular.
Playing the game
Threes has only one game mode. The object is to get high scores by combining numbers together to make 3s, then combining those to get 6s, then putting those together to get 12s, and so on. You do this by swiping on the screen to move like numbers together. But what's important to note is that a swipe moves all of the numbers on the screen at once (as long as there is room to move). With each swipe, at least one new number will also be dragged onto the playing board.
With this game mechanic, the board fills up quickly, so it is crucial to maneuver and combine like numbers (such as two 6s, or two 24s) to conserve space so you continue to have room to move. When you can no longer move or combine adjacent numbers, your game is over.
More than just numbers
While there are both math and matching aspects to the game, the real strategy comes into play when you're trying to combine for the highest number values to get the biggest high scores. You won't have the high numbers until late in the game when the board is mostly filled up, so you have to make smart moves so you don't run out of room and end the game too soon.
Fortunately, the game helps you a little bit here. Before you make a move, you can look at a little square at the top of the screen to see what kind of tile will appear with your next move.