Crackdown 2 presents more like a Crackdown 1.5 Beta than a real sequel.
Controls - 6.5
Story - 5.0
Mechanics - 5.0
Overall - 7.0
Graphics - Crackdown 2 presents virtually the exact same as the first. While slight improvements have been made and more things can be rendered on screen at once than the previous title, over all it just isn't a huge leap from the first title.
Controls - This is a major blow to the games quality. Controls sometimes feel like they are part of the challenge of playing more than the instrument of play. The inability to increase turn speed or stick sensitivity at all is a huge draw back. Many a time you'll find yourself dead or falling merely because you couldn't turn or look up fast enough.
Story - Bland and devoid of any uniqueness really. While the story it's self is pretty typical, what really hurts this games rating for story is it's location. Crackdown 2 takes place in the same city as the first game in the series. While this is a nice idea the reuse of the same city is a dangerous move. Because not done well it just gets boring. Sadly that's exactly what crackdown 2 did. You return to the same city with the same locations as before, just dirty and damaged. While this may sound interesting to some, the lack of change in the environment really feels like the entire world from the first game was just copied and pasted for the second and then just modified slightly to not be the exact same.
Mechanics - By far the greatest weakness in the game. While climbing buildings and jumping around in the first game had it's difficult moments, it seems the developers wanted to worsen this mechanic. Most of your deaths in the game will occur due to your character smashing face first into what you want him to grab onto, just to watch him do nothing and fall to his death. The mechanics of climbing and controls in general seem to be far worse than the original. Climbing buildings is sometimes just pure torture. As your character refuses to grab on to things sometimes, it's almost like the feature is temporarily deleted it becomes so bad. As well the controls mechanically are very iffy, you'll find yourself running off ledges and getting stuck on the most tedious things because the controls just do what they like. You'll be running one way and suddenly your character will freak out and go a different direction. Continuing on the bad mechanics is the auto aim. Developers need to learn if you make a game with a auto lock system, it needs to prioritize targets for you OR if you un-lock something it should pick a new target. Or give the player some way to change targets, you'll find yourself often faced with enemies of number right in your face, pull the lock on trigger only to find yourself locking onto an explosive barrel or a car hundreds of feet away while you get pounded by the many enemies right in your face. This game could have been mind blowing, but MANY bad mechanical flaws shine through. There are certainly moments where you feel like you have to fight with your character to function properly just as much as you have to fight the enemy.
Overall - What it comes down to is this. If you're a serious crackdown fan, or a serious open world fan then Crackdown 2 is worth trying before you buy it. I wouldn't say to stay away from it in any case, but Crackdown 2 really fails in some key points. While the weapon selection/car selection is good. Crackdown 2 really does feel like a Crackdown 1.5 Beta. It looks different somewhat, but many familiar locations and layouts make it feel far too much like you are playing Crackdown 1. Familiarity is good, but repetition is bad. Being just a Crackdown 1.5 would have been ok, but horrible mechanics and lacking controls make it feel more like a beta, or even an alpha. Some aspects of the mechanics, mainly climbing but other things too, feel one step away from just plain broken. My final issue with this game is the camera, climbing tall buildings is made VERY difficult just because the camera is almost over the shoulder it's so close. Combine the extreme close up camera with the extremely slow camera panning speed and you have a exploration and combat nightmare. Many things in the game, from climbing to combat are made much harder to do merely because you can barely see things at certain angles or if they move too fast.
Final Notes - There are some games out there that on their own are rather in the middle of quality, much like Crackdown 2. They sometimes save themselves with Co-Op, because while a game might be sub-par, playing it with a friend just makes it fun. Sadly, Crackdown 2 is On-line only Co-Op. I see this as a major flaw in design. We don't live in a era or economy where EVERYONE can own an Xbox. The inability to play split screen Co-Op is another part of the mechanical failure this game has. While on-line co-op is nice for some, others either don't have the money or don't have friend who have the money.