Its a surprisingly easy and effective weapon to use once you know what´s for what.
A short intro just in case is that many weapons have several different attacks that are listed in the order they come out if you attack like light 1 → light 2 → light 3 etc.
And so the simplest and easiest to understand part is heavy attack 1, it is a stab that may have the longest reach in the game ( or at least one of the very best) with a favorable angle/hitbox for headshots and the damage to make it worth using. Good for poking out armors or outright oneshotting lonely&beefier normal mobs like marauders.
You also have the push-block-attack into light 3, the notable feature of this combo is that the push attack is a downward chop with fairly good armor&headshot damage and light attack 3 is very similar.Those attacks also break shields but generally are good for damaging an elite with an accompanying squad pretty safely.
Then for the only slightly more technical horde clearing business…
Light attack 1 is a sweep that´s good for clearing unarmored hordes, you can use it, go into block to reset your attackchain and so be able to use the first light attack again to thus clear hordes at a good speed. Or alternatively you can instead use a heavy attack right after that first light attack which chains into heavy attack 2, another sweep good for hitting several targets.
It also resets your attackchain allowing you to repeat their use, which one of these you do use vs hordes is mostly preference although you might end up needing to mix things up if elites come into the horde. If they do you might wana either to try to poke them out with heavies, chip them down with light attacks or clear accompanying lesser foes by whatever means.
What i mean by chipping elites down with light attack is to make use of the fact that all of it´s light attacks have at least some armor penetration with the 3rd having the most*
So in short the Halberd doesnt have any enemy type it really struggles with the way like say dual swords does with armor, but it´s boss damage is not outstanding and it´s weak in the stagger department as far as cata goes which does hurt frontline business a bit. It also regrettably misses armor-gliding on the heavy sweep.
But overall it´s a perfectly good weapon to use even if not OP.
“Edit nr 2”
Aight just realized the halberd is bugged and it might not offer the optimal experience if you do use it, might wana hold off a while.