Well, then sadly, I have no idea what this might be, funny thing is, my second guess was also Crackdown. Well, as for hints, we know that this is a PC exclusive, and that's a hint after all ;D
Indeed. And that, together with the graphics, makes it very, very likely that it is a MMO. But I have no clue what it could be.
After looking on Moby, I'm going with Global Agenda!