I never played Crackdown (sorry!) but now seems like a good time to give it a go!
It still plays really well and hasn't dated so much, it really is a Sandbox game, you are dropped in an open world City, which has gang bosses that control various cartels. Taking out a particular Boss might disrupt the supply chain for weapons, meaning they have fewer guns, another might look after vehicles or a another might look after exposives. You wittle them away to "Clean up the city"
As you clean up the city of crime you also see the city physically become cleaner, as litter and graphitti gradually disapears.
It's pretty simple, pretty easy , doesn't really have much of a story, but is a bucket of fun.
AS the city becomes cleaner and you eradicate enemies you also gradually level your 4 abilities, this happens really gradually, you start off only being able to jump 6 feet into the air, after a few hours of play you can jump 60 feet! It really has a great feeling of progression and powering up, which is driven by collecting the 500 orbs dotted around the city, each one you collect makes you a tiny bit faster and lets you jump higher, the orbs themselves are often a traversal puzzle themselves as you might not be able to reach it with just your agility, but you may be able to find creative ways to reach them. Me and my friend used to co-op tricky orbs by one of us getting into a car, then other player would pick the car up and do a running jump and hurl the car with the other player inside.: Straight into the Orb we wanted to collect
It's great fun and super influential although it is not often given enough credit for it, it launched in jan/feb 2007.
Crackdown was one of the first games to do drop-in /drop-out co-op
It was also the game that defined what achievements are today, prior to Crackdown it was pretty much finished level 1, finish level 2, beat the game on easy.
Crackdown brought loads of little achievements to go out of your way to do or to happen by accident., "climb to the highest point in the game" "fall X metres and survive" "Pin 6 people to a car with the harpoon gun"
The orbs you collect are often imitated too, you can see the same design cropping up in later games such as Prince of Persia 2008, although in crackdown they were a core part of the game itself.
It also did updates and patching really well, they added in some free content that allows you to roam the city in god mode, spawning vehicles and explosives at will, a bit like a dev test mode, which you could also do in co-op and it brought a couple of smaller updates if you wanted some new weapons and cosmetics, all of which were useable by a co-op player who joined the game without having bought it.
There are articles about how infamous and Prototype were the 2 big superhero games of Gen8, but Crackdown was there rocking it 2.5 years before either of those released and clearly inspired them in parts.
It was one of the last big games to use Renderware, Criterion game's engine which was most famously used by all the GTA games upto and including San Andreas and the Burnout Series upto and including Paradise.