The bullet customization really floored me, there was so much you could do.
You can do pretty much anything from the basic stuff you would expect to things like having the bullets bend their trajectory, spin, adding elements, having multiple bullets fire at once while being able to customize the time of contact and property of each bullet, the list goes on and on. The list of options can be pretty overwhelming.
There were tons upon tons of combinations with kickass effects/uses. Had this really cool one that was sort of close range and spun really fast when fired, was so good at breaking boss armor.
The fact that you could go ranged at any time was such a huge plus over Mon Hun, switching between melee and ranged on the fly felt so right.