If I was going to sum up this game in a blurb, it'd be "fun but fundamentally flawed." Now, I've never played the first Crackdown, so I won't be comparing the sequel to the original. CD2 is going to have to stand on its own merits with me. And as a free-roaming mission-based sandbox game, it's... not terrible. It's even good some times. But it's never great, and the average is pulled down mightily by some things so that it's a rousing "meh." I don't really regret playing it, but I'm glad I'm finished the story, and I'm not going to bother going back to get the achievements I've missed.
Since I mentioned finishing it, I'll start with the story. There is one. Sorta. It's not really spelled out when you start, and if you're doing the bare minimum to progress through the game, you'll be most of the way done before any plot progress is achieved. There's a problem, though. The plot's stupid. I got over half the audio logs scattered around the game, so I have some of the supplementary story in the game, and it doesn't work. The basic plot is you're a member of the Agency, trying to control a viral outbreak that turns victims in to "Freaks," and you're doing that by destroying the infected with UV beacons detonated in their lairs. There's an organization called "Cell" that wants to stop you, because they think that there should be a cure for the virus, rather than just killing everyone who turns in to a Freak. And then the entire game basically revolves around you activating power networks to power beacons, setting off beacons, killing Cell members, and taking over their strongholds to use as Agency strongholds held by NPC "Peacekeepers." Fairly basic plot, doesn't constrain the players much, and allows for freedom to roam and achieve objectives in pretty much any order. Plot spoiler time (though with this game, who cares?): after detonating a bunch of beacons, someone starts breaking in to your communications channel with the Agency. Turns out it's the leader of Cell, telling you that you need to stop. Unfortunately, she never bothers to pass on a message of peace to her minions in Cell, so they keep shooting at you from that point. Supposedly the Agency has a cure for the Freak virus, but refuses to use it because after giving it to all their Agents, it made all the super-powered Agents lose their abilities and memories. The final mission proves that to be not true, since the old Agents show up. The game tries to paint Cell as a group of idealists fighting the semi-fascist Agency on behalf of the people, but it just ends up that they're all deluded, and sacrificing the lives of normal civilians to the Freaks by their unwillingness to take out the violent Freaks. And then the ending sucks and is really sequel-bait.
As for game mechanics, it's not bad. You have five skill categories: agility, strength, driving, firearms, and explosives. There's orbs scattered around that increase agility just by collecting them, renegade orbs for driving and agility that increase whichever skill when you catch it, foot/driving races that increase skill when you finish them, strength increases through punching stuff, explosives increase by using explosive-based weapons, firearms increases by shooting stuff, driving by going through stunt-rings and fancy driving, and hidden orbs that give a small boost to everything. Firearms and driving only unlock new equipment (more of which is also unlocked by taking enemy equipment back to a drop zone). Explosives unlocks new equipment, but also makes your explosives more powerful. Strength makes you punch harder and gives more health. Agility is the one likely to be the most useful, as you run faster and jump higher, and level 5 gives you the "wing suit." Basically, a glide function that works... sorta.
Bad stuff about the mechanics, though: you can get up to level 6 in the skills, but nothing happens for anything past level 5, so I don't know why they bothered with the extra level. Also, there's FIVE HUNDRED agility orbs, THREE HUNDRED hidden orbs, and then various amounts of renegade and online orbs. And you don't need even half of them in order to hit level 5 in agility or driving. It's purely there to collectathon and achievement-whore. They do give you a ping function on your radar so you can see nearby orbs, so collecting them isn't super-laborious, but once you hit level 5 in a skill, a lot of the incentive goes away to do any of the extra stuff. Explosions that don't kill someone outright sends them flying, and it takes time for them to recover. That includes you. And you're not invincible while you're knocked prone. So yes, you can get in a very bad situation if there's multiple people wielding explosive weapons, especially the homing rocket launcher. The jumping is also really floaty and hard to direct sometimes, and the ledge-grabbing doesn't work well. That wouldn't be so hard if this wasn't a city and required a lot of vertical movement, right down to one building requiring a Prince of Persia-style ascent. The controls are not NEARLY good enough for it, and you need to do it if you want to take over all the tactical locations. Some tactical locations come in sets, and if you don't capture them all in time, Cell retakes ones in the set that you've captured. The thing that will really get you is that some points require you to do some tactical elimination of surrounding Cell before starting to attempt to take the location, or else along with the extra Cell that spawn in, you WILL get overwhelmed, and it can be really annoying, since you have to respawn and restart the capture if you respawn too far away.
During all the Freak-killing and Cell-busting, your constant companion will be your Agency handler, who basically narrates everything. It's a decent enough mechanic, since it can be helpful when he points out renegade orbs or something else, and it breaks up the soundscape since the score isn't that great. Some lines get repetitive, like when he points out that you need a vehicle to get driving renegade orbs. Also, he swears at you from time to time, and talks down when you fail something, and that gets annoying really quickly, since the frustration can crank up quickly in some parts. Your main source of frustration will be the aiming system. Free aiming is basically useless. The lock-on doesn't always pick the target closest to your reticule, doesn't always swap to the next target after your current one is killed, and there's no way to jump targets while locked on. You can pick specific body parts to shoot at, which is nice, but with most guns, going for headshots at range is futile and takes longer than body shots, arm shots do basically nothing, as I never noted anyone dropping their weapon, and leg shots, while it makes someone fall over, also makes that person incredibly difficult to hit afterwards. Ninety-five per cent of the time, you'll be better off just going for body shots and pumping them full of lead. There's a UV shotgun for specifically hunting freaks, but it's aggravating too, since the range is shorter than it looks.
Worst of all, though, is sometimes, weapon-switch doesn't seem to want to work. I'll blow away some enemies with my rocket launch, then want to switch to my rifle for some close enemies, so that I don't blow myself up. Only my weapon doesn't switch, so I DO blow myself up. I've not found any rhyme nor reason to it happening, though often jumping around will then let me switch. It's the chief annoyance I've had with the game, and probably the source of most of my deaths.
With all the issues though, it is fun when you get some good weapons and can go around blowing up dozens of baddies, throwing cars, and jumping around like a fool. Ammo isn't terribly difficult to come by, switching weapons out with whatever the enemy around is using ensures a good supply, or you can get refills from safe drop zones, or by being extracted. One of the more interesting but poorly implemented mechanics though, is the idea that you're supposed to be on the law enforcement side of the equation, and there to protect people, and so there's consequences for injuring/killing civilians, even if it's just in an explosion triggered by a different explosion, or for shooting Peacekeepers. Unfortunately, most of the time, the consequences go unnoticed since there's so many bullets flying at you, or reinforcements are so far away that you don't notice when they shoot at you to "teach you a lesson."
If you can get your hands on this for cheap, either through rental or clearance, it's worth picking up and playing around with a bit, and you can get some worth out of the multiplayer if you've got XBox Live Gold. Don't count on making it your main game though, and you'll probably get tired of it long before getting everything. Really don't spend much to try it out, and go in just for some dumb fun running around, because the game's not going to get you in with any kind of narrative.