For threatening and below, Katari is my favorite class and tends to steamroll through everything.
Best unlisted skill for Katari:
Situational & Spatial awareness. Positioning for max charge knockdown effect and damage evasion. Also the strafe left and strafe right keys and camera, to curve the charge as necessary. Knowing when to and when not to engage a mob, going through unaware shielded guardians or behind them to avoid blocks. Charging through and knowing whether to follow up with a mighty blow with the camera turned, or an earthsharking / whirlwind -- or even open with an Earthshaking strike toward the enemy, then charging through them. Charging THROUGH and past the Red templar commander (or brutes) in between his whirl winds.. charging as the demon commander signals his green smoke before his pop up. Awareness is the best skill ever!
War horn is fun! But not absolutely necessary either, even on perilous. As with all DPS kits (everything except keeper really), it is highly weapon & gear dependent for higher difficulties, but the low cooldown charge and consistent knockdown means blowing through an enemy crowd, doing damage, and getting away scott free to and from the mob.
Have even more fun watching two katari charge from opposing directions in a pincher manuever, watching mobs confused which direction to swing at the katari as they're continually knocked down.
I highly recommend 2x katari if you have one already in the group. They're vastly more effective. Also with the obvious AoE CC's... Static Cage, disruption field, Abyss, Firestorm, etc.
My Preferred equipment:
Max weapon damage 2H. This is not the same as dps, because abilties like charge & mighty blow are based off weapon damage not weapon dps -- which usually means mauls like Sundering unless you have the Sulevin unique greatsword.
Heavy Armor Upgrades:+Constitution / Ranged Defense
Belt: Ranged Defense
Rings
+Charging Bull
+Heal on Kill