It's completely playable with a controller. As the person above me mentioned you CAN drop items and split stacks with the controller. I also used the steam controller configuration window to setup a new controller layer that adds bindings on my DS4 dpad for the camera zoom and mini-map zoom.

EDIT: If you are ok using mods there are two really handy mods that make weapon/quickslot changing trivial with the controller. "Equip wheel" which adds a nice graphical weapon wheel for quick switching and also "Last used weapon" which lets you swap quickly between the current weapon you're holding and the one you had equiped previously.