The first Crackdown reviews are in and it looks like Microsoft has a hit -- IGN gives the game an 8 and CVG gives it an 8.7. Here's some highlights from the reviews:

IGN -

So, you know when you start hearing the sounds of a videogame in your sleep? In my case, it was the throbbing wub-wub of a hidden blue orb, stashed somewhere deep in my subconsciousness. That's the sound of a great game. ...You'll have a blast, even if for a short while.

CVG -

Simply living inside Crackdown's gorgeous world, which is at all-times begging you to sample it's every delight, is enough for us. Chain-bomb a hundred barrels and you'll see what saints Row could have been. Scale the tallest building and you'll discover what Just Cause could never achieve. GTA IV has plenty to live up to.