Yeah, I know they're optional but DLC is kind of not optional once you buy it.
That being said, the Dark Souls 2 DLC is awful.
Crown of the Sunken King is great. It's hard and it leads to a fight with a dragon which you know you want more than anything. Also it has a boss fight with 3 NPC mobs that really gang rape you, but it's not unfair. You just need to be able to kite for 10-20 minutes.
However,
Crown of the Old Iron King is mostly fine... until you get to Iron Passage and Memory of the Old Iron King (Smelter Demon and Sir Alonne). Two VERY VERY cool bosses, 2 of my favorites... hidden behind overly long, near impossible paths with bonfires that are miles away from them.
Then you try out Crown of the Ivory King and it's like what's the point?
Dark Souls is great when you eventually see that the game has rules and doesn't cheat you at all... then you see the end of Iron King and Ivory King and you know you might as well give up.
Also, 200 hours of Dark Souls 1 and Sen's Fortress still makes me sigh.