There are plenty of other free shooters out there as well. Combat Arms suffers from poor testing and an almost complete disregard for balance, mainly due to the fact that it was developed by a Korean game developer, which is notorious for releasing poorly built games. And this is disregaring the game's stability issues on some hardware and poor netcode as well.
If you want a free tactical shooter that requires finesse and is incredibly addictive then I suggest trying Urban Terror @
http://www.urbanterror.net/news.php
It is built on ioquake3 technology, which not only makes it stable, but also very fluent for any of those experienced with similar engines.
Other free (and in most cases open source) shooters I recommend:
Alien Arena 2008
Warsow
Tremulous
Nexuiz (one of my favorites)
OpenArena
Purge Jihad
The list really does go on but those are some of the one's I enjoyed playing both as a competitive and casual gamer.
