APB is a whole lot of fun if you have a group playing together and coordinating. Yes, the missions can seem a little repetitive. However, so does any shooter in that sense. This is because the core gameplay isn't based on 'grab this shit and take it here.' The core gameplay is based on working against the opposition, outsmarting them and in turn emerging victorious.
Where the game is ruined is when peoples' Ratings get up around 200. This takes like 100 hours of gameplay, but seriously. How long is it going to take someone uber dedicated to get there? Days? Two weeks? Not too long. At this stage of the game, you essentially start unlocking explosive weapons. Rocket launchers and grenade launchers. I'll pass, because they literally blow up a car with 4 people in it with ONE shot. Stupid mechanic.