Killer is Dead is not a perfect game. Its camera is bad, its visual indicators of oncoming enemy strikes is poorly portrayed and the game is only about six hours long or so, not counting the random mini-games and odd dating sim feature where you're a male escort or something like that.
Despite the games rather egregious (or at least, disappointing) faults, it isn't by any means not fun. The satisfaction of just graphically destroying all the weird moon-robot-things is rad as hell. The visual presentation of the game and sound production only adds to that with the recurring motif of the 4th Movement of Dvorak's "From the New World" haunting you across the weird locales you end up killing people in. As long as you go into this game with the expectation of "Okay, this is another sort of flawed, wacky Suda51 Adventure" and nothing more than that, you're golden. The story absolutely doesn't make any sense and only gets zanier as the realization of "Oh, I know what you're doing, Suda, you tricky one, you." washes over you and you just start to roll with it.
Playing with a controller is absolutely mandatory. Not worth it at the $20 price point, but if you're looking for an okay hack 'n slash experience it's worth it at a 50% off sale or something like that.

Payday 2 is pretty solid as far as co-op games go.The satisfaction afforded by completing a lot of the more difficult heists is tremendous, especially when attempting the alternate routes of certain heists by doing it via stealth. Playing this game with three other friends is definitely a lot of fun and the amount of customization is fairly extensive for this sort of game.
However, the grinding aspect kills a lot of the longevity of the game if you want to invest a lot of time into it. Unlocking customization items like masks and gun parts is largely dependent on post-mission RNG, so being able to really kit out a favorite gun could be an egregiously long process given the odds of a specific gun part dropping for you. Additionally, since the differences between rushing heists and 100%ing them or stealthing them are negligible in terms of benefits (despite recent patches that alter this slightly), a lot of the uniqueness and novelty of completing some of the missions fades away very quickly when you reach the ~60ish player rank due to having to grind so much.
The combination of having to repeat certain reward-heavy missions to progress within the endgame of player level and the diminishing returns (and, ergo, satisfaction) of the actual fun parts of the game makes the game somewhat of a chore if you really want to sink a lot of time into this game.
If you're looking for a game to play with friends once in a while, Payday 2 is great. There's a solid amount of free and paid DLC that comes out fairly regularly. Definitely worth it if it's on sale. But if you're really looking for something to sink your teeth into over a long period of time, be aware of the downright offensive amounts of grinding and RNG necessary to really get all up ins on this game can be more than a little off-putting.