It's going to be a great game. Not truely MMOish, but kindof. The city has NPC characters running around their daily business like GTA, and players are dynamically matched. Criminals commit some kind of crime, be it murder or stealing TVs or robbing an armored car or bank, and then the game takes equally skilled players and sends them an "All Points Bulletin" hence the name of the game, and pits them against you to stop your crime. Or visa versa if you play the law.
There will be up to 100+ players in any one city zone and the rest will be the npc city population. I don't know if you progress to higher zones or what but there are lots of zones.
The level of customization is unprecidented in a game, down to the fact that you can cut and comb individual subsections of hair, and put tatoos and scars anywhere, not just in preset slots. You can mix and combine all sorts of imagery for unique tatoos or clothes designs and there's talk of being able to sell your designs to other players. Car customization is just as extensive. There are all kinds of crazy interesting rumors about the game, but most of that I typed is from the articles or youtube vids.
Looking forward to this game very much, though not as much as MAG which might slake my thirst until the next Planetside game comes out