ok Urban Terror is a fightning game you can download it here http://www.urbanterror.net/page.php?6 but the follow what it says when on the site if you dont then the game might not work.
Its Online game you have different weapons better than halo.
Note: Whiles playing it close every thing that got to do with internet so you wont lose contection to online game whiles playing it thats all
All the rest info is on the site please follow them.
And i hope you enjoy the gameXD