Allow me to interject on Cass, her Q speeds her up and her E has low but mounting damage on a low cooldown. Combo'd together, it gives her this feeling of being a slippery as fuck snake zipping around the combat field, orb walking between skillshots. Her W stops dashes which feels cool to hit, and her ult also has a pretty cool flash mechanic on it, and you have to make sure that you're facing your enem to make it work which is a whole nother mind game.
Now, I've only played Xerath once, but I'll take a stab at it. The long range on his W and E, and the charge-up on his super long and narrow Q make him feel like an artillery cannon, and there's nothing as cool as using his ult, you can almost hear the "ORBITAL CANNON FIRING".
Garen is the most boring fucking champion in this entire game. He's just a sword guy. At least Pantheon has the mandrop.
Brand suffers from almost the same issue. All his abilities don't really scream "Fire". If you changed all his abilities to some ambiguous magic, and gave him one of Ryze's old model's it honestly wouldn't feel that different. There's nothing really even satisfying about him. You just walk up, missdrop all your abilities and walk out on half mana until they come back up.