Rarely does a game with such a boring name and such a boring premise turn out to be so damn addictive.
SpaceChem is a puzzle game that appears initially frightening, heavy on scientific terminology and symbols, but persevere and you'll soon find it's one of the more polished and addictive puzzle games in recent memory. It's certainly got the most rousing soundtrack.
It's available for $US20 from the developer's site, but you can grab a demo now if you want to give it a spin.
A warning: we're not kidding with the science stuff. For a puzzler, normally the simplest and most accessible of genres, this one will take some notes and some repeat play.