One of the abilities the two new protagonists of Army of Two: The Devil's Cartel get is called Overkill. After filling up the Overkill meter from in-game actions such as killing others, a player can activate it to slow things down, recover health, and blow up EVERYTHING. Overkill gives a explosive effect to your bullets, and nothing stands a chance against your rampage when it's activated.
Each player gets there own Overkill meter, but only one person needs to activate it to turn on the ability for both players to use it. A good tactic is for one player to activate theirs, and then have the other player turn their's on after the first one runs out. Both players can activate Overkill at the same time too, which gives an overall bigger impact from the ability.
Generally, it will take players in the final game a while to fill up the Overkill meter, making it precious resource. For the press demo though, it was filling up constantly so we could see the feature as much as needed, something that I was more than happy to abuse. It was pretty cool seeing the environment get shredded, and see limbs get ripped off bodies in my attacks.
Another thing about the new Army of Two I liked was the cover mechanics. You simply need to look at an object that you can take cover behind, press the cover button, and the game will take care of the rest. Your character will automatically do what needs to be done to make his way to the desired cover destination. You're not locked into the run, so you can pull back on the left stick to break the run if you change your mind.
Overall what I played felt like your standard third-person shooter experience. It certainly looked great visually thanks to the Frostbite 2 engine, just nothing really wowed me from the demo. It definitely had that Army of Two feel going on, which I'm still not sure if that's a good or bad thing.