I would also like to note just how much I'm loving the full game. In some ways the game is a step down from the demo because the demo allowed you to power up significantly faster and thus you could max out all of your skills (if only one or two of them per play-through). So the full game is slower in that regard.
HOWEVER, the full game also benefits from that because it's so addicitve trying to level up each skill. I've also found the boss fights to be a lot more fun. While the bosses themseles are absolute wimps, trying to break into their stronghold with a rocket launcher and high agility has provided some of the greatest thrills I've ever had in a game. It may be true that there isn't much meat to the game and it's super short (I'm taking it slow and I've beaten the first 2 islands in 7.5 hours), but it provides some of the most unabashed pure additive fun that I've had from ages. The only thing preventing me from buying it for $50+ is that it will inevatably drop in price and it's short enough that I could beat it in a rental and then buy it after a few months.
On a side note, I hated GTA, but love Crackdown. It's like they took everything that sucked about GTA (the controls, shitty dialogue) and cut that out. Brilliant game!