Happy Glass is a challenging puzzle game that I've been playing for a while now. The basic idea is that you have an empty glass and a water pipe that shoots out water. The goal is to get the water into the glass, by drawing lines, shapes, etc on the playing area. Let's look at an example.
So we have a water pipe at the top left, and a discontented, empty glass at the bottom right. But there's a pit between them. If the water runs out as things stand now, it will fall into the pit, and the glass will still be sad.
The simplest solution is to draw a line over the pit, like so.
The water flows over the line, down to the glass, fills it up, and the glass is happy. All is right in the world.
So that's the basic idea. Seems simple, right? It certainly starts out that way, but the complexity ramps up the farther you get. That example above was level 2. Let's take a look at level 461.
So the first problem we have is that there's nothing supporting the glass. So if we don't do anything about that, the glass will fall off screen into the abyss, I assume to be melted down and used for glass blowing demonstrations at a historical reenactment village.
The second problem is that those blocks are in the way of the water flow. If we don't do something about that, the water will flow off to the sides and miss the glass, leaving the glass unfulfilled. You will question your life choices, your significant other will start shopping around for someone who can get the job done, and your children, realizing there's nothing more they can learn from you, will head to the Far East to drive a taxi cab while they search for fortune and glory. But I suppose that's the worst case scenario.
I won't spoil the solution for you, but I will say that this has been a very challenging and rewarding game so far. There are plenty of levels to keep you engaged, and they throw enough new concepts in to keep it interesting. The physics engine in it is quality; water falls and flows realistically, and you can draw basically any shape you want and it will fall, swing, and flip around like it would in real life. I think it's the freedom to draw anything that really sets this game apart. There are multiple possible solutions to each level and you can try crazy stuff just to see what happens.
So if you like puzzle games that are a bit different, this is one of the most engaging I've ever played, and I'd recommend giving it a shot.
It's available for both Android and iOS.