This is a great multiplayer game. Missions are limited but they sure are fun and have their own secrets. I recommend it.
There are a couple missions with 'First World Bank Heist' and 'Diamond Heist' being the popular amongst most players; reasons vary through the fun of the levels, the sneaking intensity and the hidden secrets and achievements.
While playing, the player can start to build in his or her category as well as have the ability to max out all the categories. When players start to advance in each category, they start to unlock new weapons, tools and upgrades for weapons, tools and themselves (which is reflected through boosts).
The skilling meter is represented through a player's reputation level.
This game has a great Downloadable Content (DLC) that adds an entire new reputation class, weapons, tools and 2 new maps/missions.
With the level this game achieved in being a heist / Left 4 Dead simulator; it is expected that Payday 2, planned to be a full heist simulator (with a bit of Left 4 Dead), will be another great multiplayer hit by Overkill Studios.
I recommend this game.