Got it today. Amazing...
I couldn't put it down for a second. I just started to explore the first island when I when I started. (Damn there's a lot of stuff to climb on)
Then I did some missions and got to the part where you restore power to the first part of the city. After that I decided to work on my ninja skills. :P
I just got off like 20 mins ago, so far there has been a limitless amount of things to do.
My apologies for the crammed up post - on my PSP. :/