I really love Kol too but I wasn't sad when he died... just angry lol. Like Tommy said, Originals are like Vampire gods. But because of stupid plot convenience, Elena and Jeremy managed to kill him.
Klaus took and entire army of Vampires by himself. So did Elijah. Even Rebekah could fight Aya and many Strix members ( who are mostly very old vampires ), But Kol died to those weaklings... Honestly, I don't mind a character being killed off... But at least, make it believable.