As you can see by my playing time, I beat the whole game and in no case I would recommend this game.
Don't get blended by the graphics and buy Crazy Machines 1, Crazy Machines 2, The Incredible Machine or if your kid is just 6 years old Crazy Machines 1.5.
There are 3 terrible terrible mistakes in this game:
1) Inconsistent Physics: Imagine an object is flying on the left side of the screen. It always has the same trajectory, but if you place an element on the bottom right corner, which doesn't interfere with the other object, suddenly the trajectory changes and making it often impossible/very difficult to finish the task.
2) The grid on which you place your elements is way too big, causing a lot of unnecessary trouble. Imagine your idea/plan is absolutely correct, but you cannot execute it, because the laserbeam misses your mirror by 2 length-units, but you can move the mirror in the grid only by 10 length-units, causing the beam to miss your mirror again. This makes a lot of trial&error work necessary, even though it could have been easily avoided. In no other Crazy Machines game this was as annoying as here.
3) And that is the absolute deal-breaker here. You get punished if your solution is more intelligent than the default solution. The rewards are not task-based (the less you use, the better), but instead path-based. This means you have to place objects the way the game thought for you. Because if you don't, the trajectory of objects might be different and you won't be able to collect the cogs in the level. This is such a horrible design choice, I can't imagine why any sane developer would make this.
There is also something other bothering me and that was the "help". By looking at the shape of the background you can instantly see what object has to be placed. For example mirrors belong onto circle-shaped wood and generators on square-shaped wood. This dumbs the game down and no, that's not suitable for very young children, because Crazy Machines 1.5 makes it right. In that game are easier tasks, and more puzzles in between, so the difficulty doesn't rise too fast, but it does not dumb the puzzles down.
Stay away from this game and don't bother playing it. Get the other games I listed in the beginning of the review.