DeathscytheX

Its made by the makers of L4D. Its a 4 man team, but instead of zombies you are pulling off heists and fighting off cops. The twist come in where you cant kill civilians who are annoyingly stupid and run in front of cops and what not. In the first game it cost you a respawn time penalty, in 2 it costs you a good chuck of cash from your final possible payout each time you do it.

Some of the heists give you the option to pull the majority off stealthy, but that requires 4 coordinated real players... the AI are dumb as rocks. When the cops show up, every 30 seconds or so an assault wave begins where their attack intensifies. The cops are more aggressive, and specialized cops come in with riot shields, tasers, and the Bulldozer which has full body armor an can only be taken down with multiple headshots.

The first one was insanely hard, and I could only beat 2-3 of the heists, but you would keep all of your XP even after failing, in the second game, you hardly get anything for losing, but the missions are beatable while still maintaining difficulty. The class skill trees are more advanced, and you can buy and upgrade various weapons. The first game had less weapons with no upgrades, and you unlocked them through leveling up.