Netrek is the probably the first video game which can accurately be described as a "sport." It has more in common with basketball than with arcade games or Quake. Its vast and expanding array of tactics and strategies allows for many different play styles; the best players are the ones who think fastest, not necessarily the ones who twitch most effectively. It can be enjoyed as a twitch game, since the dogfighting system is extremely robust, but the things that really set Netrek apart from other video games are the team and strategic aspects. Team play is dynamic and varied, with roles constantly changing as the game state changes. Strategic play is explored in organized league games; after 9+ years of league play, strategies are still being invented and refined.
The game itself has existed for over 15 years, and has a solid playerbase, including some people who have been playing for nearly as long as the game has existed.
All netrek clients and servers are completely free of charge, although there are several people working on commercial netrek variants or derivatives.
I dooshed Dave +6 yesterday while playing netrek.