A great co-op game, if flawed. Avoid the single player portion of this game.
As you commit the aforementioned crimes, you gain money and XP, which earns you skill points. In this game, cash is king; you will need it to improve your character in ways such as purchasing new weapons, altering your mask, adding attachments to your weapon, purchasing assets for use in a mission (such as an ammo drop or floodlights in a dark environment), and purchasing new skills for your character (which also uses a skill point, earned by leveling up. Skills are broken into four trees, or classes: Mastermind, Enforcer, Technician, and Ghost. The Mastermind is a master of manipulation of guards and civilians, the Enforcer is the go-to guy when the bullets start flying, the Technician is an expert in drilling vaults and using explosives, and the Ghost is the stealth master. You may purchase skills from any of the trees, allowing you to mix and match abilities from multiple classes.
Each of the missions is slightly different each time you play it, adding some replayability. One playthrough, the security camera may be in one spot. On the next time through, there may be no camera there, but the security room moved into a different part of the bank.
If you plan to play primarily in single-player, it's probably best to avoid Payday 2. The AI is barely functional, and the only thing they are good for is shooting and getting shot at. They will not help carry bags of loot, they will not help destroy security cameras, and they will not help place or repair drills. The lack of assistance from the AI means that in single player, only the easier missions will actually be achievable.
If you can find some people to play with, Payday 2 is one of the best co-op experiences available on this generation of consoles. Having different classes in a group means each person has a specific role to fill within the team, and success hinges on your ability to work together and utilize the different advantages offered by each player. It's a great feeling when everyone works together to successfully complete a heist without anyone alerting the police.
The game has a few annoying glitches and questionable design choices that make the game slightly less enjoyable than it could be. After completion of each mission, you unlock a "Payday card". These Payday cards can be a weapon attachment, mask customization options, or bonus cash. Since this is the only way to unlock the various attachments and mask options, it can be frustrating if you're wanting a specific attachment and the RNG decides you can't have it. On top of that, once you unlock the attachment (you only unlock one per card, meaning you may put the attachment on a single gun), you must pay to attach it to a weapon. If you decide to remove the attachment and put it on a different weapon, it costs you money again, and then if you decide you really want it on the original weapon, you have to pay up again. This system discourages experimentation and, early in the game, forces you to commit to a specific loadout until you get further into the game and can earn money more rapidly.
Other issues include occasionally poor hit detection, suicidal civilian AI who sometimes stand up when you're shooting just over their head at a SWAT member or run into the middle of a firefight with no regard for their own safety. I have encountered one glitch where a teammate was able to walk through a closed vault door, and there is another glitch that makes a specific mask pattern appear more often than it should in Payday cards.
All in all, a great co-op game if you have people to play with or if you can easily make friends online. This is easily one of the best co-op games this generation and is well worth the price of admission.