I have been playing through this game, I'm up to and around 20 hours, and it is just so goddamn addictive! I consider this game (Along with Chrono Trigger DS and Castlevania: Order of Ecclesia) to be the best game on the DS, period. This game not only does what San Andreas did (Minus the Airplanes/Helicopters, unless I haven't gotten there yet >_>) but it also does **** that both just isn't possible on the consoles and wouldn't work for characters like Niko or CJ.
Seriously, if you have a DS collecting dust or your still playing Chrono Trigger, take some time and pick up Chinatown Wars.