Your goal is twofold: Rebuild each of the 500+ levels of the station while stamping out the bugs. There are no time limits (at least, there weren't in the first forty-odd levels I played). There's little direct targeting of bugs. Instead, you shoot lines that seal off sections of the station. If you trap bugs inside, the bugs are smushed--but if the lines don't completely extend before a bug gets to them, your lines become insect chow.
It's a simple premise, one that requires just a screen of information and no practice levels to get started. However, as you work your way through the station, the levels get more complicated. Some areas are easy to seal off; others take careful timing. Some insects crawl along the girders, and other sail through the open spaces. The bugs' different rates and gaits make it a challenge to figure out which ones you can seal up, and when. An array of power-ups--freeze, missiles, slow-motion, and more--give you an edge if used wisely. But be warned, the bugs get some power-ups, too.
One thing that made Cosmic Bugs especially enjoyable for me is that it takes coordination without requiring breathless concentration on the trigger finger. Cosmic Bugs is quite stimulating--particularly if you leave the heart-pounding soundtrack on--but the lack of time limits lets you sit back and take your shots at your own pace. It's a lot of fun without the tension all too common in real-time games.