You face three different gangs in Empire City: the Reapers in the Neon (first island); the Dust Men in the Warren (second island); and the First Sons in the Historic District (third island). While the gangs get tougher as you progress, the gang members are all roughly the same types.
Gunner[edit]
The average gang member is equipped with a rifle and is a crack shot. Really. These guys must all be ex-military snipers. They can hit you from two or three city blocks distance – further than you can actually see them. It's pretty irritating. When bullets start flying, press 
to try to see a flash of red that will indicate where the rifleman is, and then take cover and try to snipe him back. About halfway through the game, you get your own sniping Power (called Precision) that will put you on a more even footing.
Bomber[edit]
These gang members, in addition to shooting at you, will throw dynamite. It takes them a second or two to light up a stick, which gives you a chance to shoot them before they throw it. You can also use Shockwave to deflect the dynamite back at them.
Machine gunner[edit]
Machine gunners come in three types: foot soldiers, carrying a machine gun; turret gunners stationed at a stationary turret with shielding; and turret trucks, which are a flatbed truck with a turret on the back. Whenever bullets start flying at insane speeds, find cover fast and identify the turret. Once you have the Precision Power, taking out a machine gunner involves finding a good line-of-sight and using Precision to head shot the gunner. Prior to that, your best bet is to run for high ground and try taking out the gunner from above with Shock Grenades or Thunder Drop or just raining Lightning Bolts down. For turret trucks, you can also target the truck itself and blow it up.
If you have the Guardian (Good) upgrade of the Megawatt Hammer , you also can fire a Megawatt Hammer above the turret, then aim at the gunner and press 
to redirect your rocket, avoiding the turret's shielding if you time it right.
RPG[edit]
Instead of a rifle, RPGs carry a rocket propelled grenade launcher. Deflect the grenades with Shockwave and shoot the bums. RPGs are generally larger and slower than regular gang members, making them easy to pick out of the crowd. Always take them out first (unless you're dealing with a kamikaze or Conduit).
Kamikaze[edit]
These bozos light up a bunch of dynamite and then run at you. Shoot them or Shockwave them before they get close or you're a goner.
Conduit[edit]
Conduits are super-powered gang members. Each gang has its own type of Conduit.
Reaper[edit]
The Reaper Conduit has two basic abilities: teleportation and shockwave. They can zip around the battlefield unless you keep them off-balance, and they can release a shockwave that tears up the ground in front of them. Fortunately, you can see and hear the shockwave coming, giving you a chance to roll out of the way. Try to Shockwave these Conduits to stun them, and then fill them with Lightning Bolts.
Dust Men[edit]
There are two types of Dust Men Conduits.
First you'll meet a guy wearing a suit of trash. He carries an RPG and spawns scorpion robots made of trash. The scorpions aren't much trouble; though, they can hurt you if they gang up on you. The grenades definitely are trouble. Use Shockwave to deflect grenades and maintain a steady fire on the Conduit. Use Megawatt Hammers or Grenades if you can as they will also destroy his scorpion bots.
Second is a giant trashbot. This thing shoots a machine gun, uses a shockwave and blasts you with meteors made of trash. You first fight one as part of a story mission; thereafter, you'll meet them with regularity. Take their arms off with Lightning Bolts and then fill them with Grenades. They are much easier once you have Polarity Wall. Until then, you have to run in circles to avoid the machine guns.
First Sons[edit]
First Son Conduits also come in two types, and one is particularly nasty.
The first First Son Conduit you meet turns into a large, neon-purple, semi-transparent giant. These massive Conduits can do a lot of damage; but, they only have melee ability and they're slow. Fill them with Bolts until they revert to normal size and then take them down.
The second First Son Conduit is quite a bit worse. They are invisible warriors who will momentarily become visible in order to shoot you with a shotgun. They typically materialize right next to you and they almost can't miss. Usually, an encounter with these guys ends in death the first time you run into them on a mission. Once you know where they're going to start hitting you, you can pepper the area with Grenades and wait for them to be shocked into visibility. Then you can shoot them.