Crackdown is certainly no technical slouch, and nothing demonstrates this like the tower's summit. Screenshots bring the game's relatively low-detail, cel-shaded graphical style into sharp focus, but first-hand exposure reveals an incredibly solid frame rate, unprecedented draw distance, an amazing volume of NPCs whose design, behaviour and animation can't be called into question, along with a lighting system that cycles the days happily alongside your quest for justice. In other words, I'd be surprised if there was disappointment, although if I encountered someone who found it so, I would probably just pat them on the back consolingly with a limpet mine, leap 400 metres in the opposite direction and press the "detonate" button....
Crackdown is more like Naughty Dog's Jak II approach: we're videogame characters, wouldn't it be fun if we had a whole city to play with? Within this construct, things like minor control niggles (you can't cycle between locked-on targets) and the occasional glitch (co-op is sometimes tricky to get going, and some boss sections fail to trigger properly online, meaning you end up running around empty venues, bizarrely) are trivialities. It's telling that the biggest complaint I have is that you're reliant on those Achievement Unlocked notifications to tally up your kills and feats, with no GTA-style stats page to call upon. Think about it: I'm upset with Crackdown because I can't examine how much fun I'm having in periscopic detail.
It's also rather short. I blasted merrily through everything central to the game in a day, and mopped up most of the rest by the end of a weekend. Being able to pick and leap into any of your friends' or even complete strangers' cities is likely to keep that buzz going though, as will the Time Trials (beat bosses quickly), the wealth of sub-achievements, and the prospect of downloadable content, some of which we know will be free.
In other words, being so excellent that you obliterate the single-player in a weekend is not enough to stop it being my favorite Xbox 360 game of recent times. You should definitely buy it, because, on this evidence, waiting for Grand Theft Auto IV would be rather daft. This is what it should do anyway.