as it's all tied to a random card choice at the end of each mission.
ME3 much ?
ME3 handled this a lot better by basically following the trading card game model. With all those extra packs available, I have at least a slight measure of control over what I will get.
At the end of each heist in Payday 2, you are presented with three face-down cards, of which you can choose one. These cards can be equipment unlocks, they can be various cosmetic items, it can be an EXP or cash boost. As far as I am concerned, this "choose a card" step is completely unnecessary, since there is no way to make an educated choice (Unlike the booster packs in ME3 multi!).
The second thing that I dislike about this is that these cards only unlock equipment in the store that you can buy later (at hilariously inflated prices). In ME3, when you got a good weapon, you were able to try it out immediately. Here, you will have to grind through one, if not several, heists in order to get the cash to try something new; This is also true for skills.
Basically, Payday 2 uses money as a limited ressource you have to grind a long, long time for in order to do even basic stuff like leveling your character. It's gating the content to a degree only seen in the F2P realm, and it's completely baffling as to why.