Never played the first game, but Payday 2 does offer some options making it playable enough offline (solo) or with up to 3 others for different heists or other mission types. There are a billion stealth games out there but not too many where stealth vs guns blazing are equally compelling or balanced options - P2 tries to get this right, but save for the best players, full stealth is often REALLY tough (one mistake and you're going loud) and it's relatively safe to assume you're going into a firefight at some point every mission, especially before you have access to improved skills. Then again, some missions have you destroying mall property or torching / stealing guns from cartels, and survival is the point from the get-go.

imo playing solo is totally viable, but the AIs only target enemy shooters and won't perform actions relating to looting, hostages, operating drills, etc so trying to do things like get 6+ bags of loot from a store to a faraway van or looting safe deposit boxes are far tougher. On the other hand, the AI players seem to be pretty much invincible unless enough cops are close enough to melee / apprehend them, so they can take all the bullets you need them to.

The diff curve is probably higher than most games of this type if you jump right in, but you can try out the Safehouse level to learn the mechanics. There are plenty of COD'esque unlocks as you complete missions and earn cash / XP, both in skills and equipment, some of which is just character customization. If you play enough to reach lvl 100+ you can open up the Infamy track for even greater rewards.

The random chatter by Bain and the other mission NPCs is pretty good throughout and does a good job of cueing you to events and changes in the mission. The music does an excellent job of matching the tension and action of stealth vs loud missions (though having more guard chatter / cues as to when they move around would add immersion and functionality), and there's a fair amount of randomness in things like whether doors are locked / placement of guards / vaults, which definitely adds to replay value but can be frustrating if you want to repeat a failed level to get it right with all the variables the same as before. I do like that occasionally a job will take an extra day to escape if you've taken a long time; it adds an extra feel of reaction based on your performance and helps mix things up.

P2 definitely needs some more mission types, but the difficulty options and built-in random elements will keep you playing awhile. If you can find a few friends and specialize up your skill trees you'll have the best shot at advancing through teamwork, once you begin working together as a unit. But inevitably you'll be doing plenty of levels over while you get the hang of things. Be prepared to be frustrated, but you'll have memorable moments of close calls and huge payoffs if you stick with it and master your skills.