The basic rules are pretty straightforward, but the game does some amazing things with it. There's a
demo on Steam that should give you a pretty good idea of whether you'll like it or not. It covers the basics of the game, and from what I remember, the point where the game opens up into "mind-blowing" territory.
The thing to keep in mind about the game is that, for all of its perceived complexity, there's very little "structure" to it. All you have is input chemicals that the game gives you and X number of output chemicals that you have to produce to succeed. Other than that, there aren't very many "limits", so there's a gigantic amount of creativity in how you can approach solving the levels. So much so that after the end of every level the game compares how long your solution took to run, how many pieces you used to solve it, and so on to everybody else who's played the game. You can spend so much time on a particular solution, though, that even if it's horribly inefficient and takes forever to run, you love it all the same because it's
yours. I spent days working on a solution for one of the extra, TF2-themed puzzles, and my scores were some of the worst in the world, but the solution still counts, and I loved my little kludge all the more.