Is it just me, or is the Warlock seriously underrated?

I play an Orc Warlock, and it's quite difficult to lose a fight as long as I have fear. Even hunters I'm not afraid of; I just have my voidwalker take the damage from the pet and I just keep casting fear on the hunter after casting Curse of Weakness. Everyone keeps complaining that a Warlock has no defense, and they're the worst class in the game... am I missing something?

I'm only a lvl 23, so I still have yet to see what kind of attacks will be coming after me in higher levels, so if someone could please enlighten me as to why spamming fear isn't the best thing ever! (oh, and btw, undead are NOT immune to fear. I just wasted a lvl 27 undead mage yesterday; all I did was spam fear. It was f*$#& hilarious, and he was sooo pissed. )