I started wishing I could play it on my computer, which led me to the conceit you read before you: a Crackdown MMO would do me nicely. Think of it: play as an agent of, well, The Agency, the law enforcement entity of this world. Or, positing that the enhancement program that fuels the special abilities of Agency officers is stolen and sold on the open market, play as one of the 3 rival crime syndicates instead. PvP is built right in!
Eschewing the typical menu-driven improvement interface of your standard MMO, you would choose which of your abilities to improve on-the-fly, as it were. See a location you'd like to explore, but can't quite reach yet? Best get to work on your Agility, then, soldier!
As law enforcement, you could choose from a wide range of missions, from escorting VIPs around, to removing a local kingpin, to multiplayer compound raids. As criminal muscle, pretty much the same range of activities await, with the extra incentive of taking out your rivals, thus procuring more turf for your side.
I'm disappointed that more wasn't made of this game. A lot of people seemed to like it as a proof-of-concept vehicle more than a finished game. But there's still room to grow -- Realtime Worlds, are you listening?