The combat is pretty sweet! First you lock on and then you can adjust your aim to shoot certain body parts. Skillfull shooting gets you balls. Balls make you rage (cos they are sweaty and smell of cheese). When you rage you go into first person, invincible with unlimited ammo and the aim is guided and easy. Rage lasts about 15 seconds I believe.
Cops and Gangs. When you do bad things like steal cars and do hit'n'runs your visibility meter increases. When it's increased cops will want to talk to you and will follow you. If you don't stop the visibility keeps going up unless you escape by ditching your car or sneaking into a back alley. If you choose to talk to the cops you have a small chance to lower your heat and a large chance to lose all your coca cola and dirty money. If your visibility maxes you will be wanted. In order to escape you have to go out of their range, a system like that of GTA4.
If you kill drug dealers and gang members, your gang heat goes up. Gang heat means that you can't sell coca cola for as large a price as you can when it's low or nil (selling a gram of cocaine for 100 dollars is amusing). Successful drug deals decrease gang heat. You can take gangs out, they are marked by a skull on the map and are usually in back alleys. Your heat will increase with every member you kill but then it will decrease slightly after you eliminate a gang. You can choose the passive path though and intimidate gangs which will also reduce your heat. You taunt them and then they will want to talk to you. A bit like talking to a cop but a bit easier. You can pay to reduce both cop heat and gang heat.