It is often mentioned that many games are not available on Linux. While several big titles are indeed missing such Linux ports, the Open Source community itself produced some impressive titles. Here is a short list together with some promo videos.
Most of the Linux Distributions out there are shipped with the set of games included in GNOME or KDE. These games are nice for short breaks, but not comparable with big, hour consuming games sold by the big publishers. However, the Open Source community stepped up there to deliver its own products, and many of them are not only interesting, but simply impressive. Also, there is a game for almost every taste available.
First of all the games where I also found a promo video:
The first person shooter Nexuiz speaks for itself: