Well I'll explain 'em both a bit. ('cause I'm bored xD)
Urban Reign is about a guy named Brad Hawk who is hired by a girl named Shun Ying. Wait, lemme go back. This guy from a streetgang called the Zaps, (the guts name is KG by the way) and Shun Ying is blamed for it. So the Zaps leader, Dwayne, declares war one them. You go around doing various missions for Shun Ying to prove she's innocent.
So I think on mission 60, we find out that Shun Ying is innocent. Another group called the Outlaws (I believe that's their name) are the ones responsible. So while everyone is helping take care of KG, the Outlaws destroy the city.
20 or so missions later, we find out that the mayor, who we know as Bordin, is responsible for EVERYTHING! It's a really great game :3
Then Urban Chaos: Riot Response is a first person shooting game. You, Nick Mason, is part of an elite squad of police enforcers called T-Zero. You're hired to help take back the city from which is being taken over by a group of malicious killing gang called the Burners. You get a great arsenal of weapons which can be upgraded throughout the game. The weapons start as a standard police pistol and stun gun then eventually a prototype Shotgun and machine gun. After unlocking all medals (You achieve those by capturing Burners by using your taser, getting headshots, not using a checkpoint and getting all "gang masks" hidden throughout the level), you get a motherfrickin' MINIGUN!!!! xD
Both are great games. You really should look 'em up on yiutube :3