Where's My Water? - picked up through an App Store promotion. It is really outstanding, and it forces you to sit back and think...and think...and think...and when you got the perfect plan, the plan blows up in your face and you have to figure out another way to do it. There's hundreds of puzzles, plus bonus ones laying around when you find some stuff hidden throughout the levels. Also some achievements....that are not as easy as they sounds. Your kids will be playing it for hours.
I know I was.
Edit: To fill you in on the details. The objective is simple. You are helping a alligator named Swampy find some fresh water so he can take a bath. In each level, there will be water you have to get from Point A to Point B.
Sounds easy right? What makes this challenging is that to advance further in the game, you have to collect 3 ducks scattered on each level. The ducks are in some precarious positions, sometimes off the beaten path, and you have to run enough water (and only water...bad things happen if they come in contact with anything else) over them to obtain the duck (then complete the level with it in tact). To add another twist, the player will be introduced to various elements throughout the game that will manipulate that water in some way or form. Turn it into poison, evaporate into water vapor, grow plants, etc. Mines are in place, and the elements can sometimes act upon each other...
In short, three simple things to remember.
1) Get as much water as you can into the bathtub.
2) If you run out of fresh water, you lose and have to start the level over again.
3) If a drop of anything but water ends up in the bathtub with Swampy, you lose and have to start the level over again.