Holy heck yes, yes and YES.
The DLC is some of the best stuff in the game. Best bosses, best areas. Hell, I'd even rate the areas as some of the best in any souls game. The way you get to actually play around with level geometry is really cool and the design is far more intricate than prior DkS2 areas. It's a lot more similar to BB in that respect with ingenious short cuts. No duds at all here. Seriously, I'd rate the DLC above Artorias. Sure, no boss fight is as good as Artorias but it also doesn't have a single bland area (and the woods in the DkS1 DLC were only really cool from a lore perspective).
Absolutely worth it I'd say. Only issue is that you need to defeat certain bosses in the base game in order to access them. That necessitates a few hours of replaying for some. Not much if you've done it before but enough to be slightly annoying.