Recs.
Updated
SpaceChem is a design-based puzzle game about building machines and fighting monsters. It costs $9.99.
The main concept of the game is to produce specific chemical molecules through an assembly line by programming manipulators.
SpecsUpdate
Pros
Pro Allows for short or long play sessions
The gameplay allows for a player to come in and solve a single puzzle in a short amount of time or to sit and tinker with a puzzle for hours trying to devise the perfect solution and contraption. It all comes down to what one want to put into the game but the free form of the puzzle solving is what makes it great for anyones playstyle be it short or long.
Pro Endless gameplay through user created solutions
An individual players choices of components, arrangements or factories used will result in completely different experiences and problems/puzzles when compared to another users experience. A truly individualized experience that expands the games replayability.