One of the best puzzle game ever made !!
A real challenging brain teaser where you have to deserve to see the end !
A simple concept and goal in a total freedom environment !

Story (summary) :
You start as a kind of "hostage slave" who has to build stuff for an alien race.
Then, you get saved by the allies and have to help them build other stuff to fight back the kidnappers.
Finally, you need to build again to return safely to Earth.

Game Length :
I just finished it and it tooks me 72 hours to complete @ 100% (every single level + all achievements).
The workshop feature allows you to play hundreds additionnal maps made by players !

Another masterpiece for the company who made SpaceChem ; a must have to any puzzle lover, worth every penny even at full price !
Extremely recommanded !