Stuff that modifies or at least allow you to modify the core Gameplay.

Spam Mod: A huge downgrade for me is that the Devastator's and Sniper Rifle's Scoped View is momentarily removed when you fire these Weapons, whereas in Vanilla SS4, you just stay inside the Scope. This has been so annoying to deal with, and it's a shame as there's a fun Exploit where you don't have to reload/wait for the animation of certain Weapons such as the Shotguns when you go in Dual Wield Mode immediately after firing, so for the Double Shotguns, you could dish out 6 Shells in less than a second thanks to this Exploit. Broken and not the "Vanilla Challenge" that I usually want, but fun nonetheless and it's a rather subtle Exploit that makes it not so broken.