Crackdown 2 is immense fun, especially when played with up to four people at once, but once the game is completed and you have control of the city what is there to do? The Achievements in the game are a great way to increase the lifespan and there are a few that are great fun to do together. Not all of these achievements are officially co-op based, but by working together you can make the tasks a lot easier.
The Basics - 380G
Complete the entire game and capture all locations and you should come away with 380 Achievement Points. In theory only the player who hosts the game gets the achievement, but if you create one save file that you use only when playing with the same friend, you should both unlock the achievements.
Pebble Dash - 10G
Once the basics are over you can go for the more entertaining achievements. Hopefully by this point you would have at least level 4 in all skills, but you probably need level 5 in agility and strength to really work the Achievement System. Pebble Dash is a fun achievement to get and is even better in co-op. It requires that you reach the very top of the Agency Tower and jump into a nearby chimney for a convenient surprise. However, getting up to the top of the Tower is painful when tried alone. The secret is for two or more player to work together!
To one side of the Agency Tower is a helicopter pad that has 4 helicopters parked up. One player should pilot a chopper, whilst the other players sit on the seats that are on the side. This allows you to be air lifted to the top of the tower rather than having to jump up. From there it’s a matter of delicately dropping off you co-op partners and watching them jump to victory.