Yeah, the DLC is definitely worth it. It has four chapters that are a bit longer than the ones in the base game and eight new major bosses, plus a good variety of equipment and consumables and costumes and all that good stuff. If you liked the base game, I highly recommend getting the DLC.

I just beat it, it's a good chunk of content. I'd say about 50-60% of the base game in terms of areas to go through. It's well designed, there are plenty of new enemies and interesting weapons, a lot of good outfits, a new layer of p-organ upgrade, and some of the best bosses in the entire game. The story is good and interesting, and it sheds a lot of light on the overall story. Honestly, I don't think you'll be disappointed. It's very much akin to the old dark souls DLCs, and I'll be going through it every time I play this game for sure.

the others have said most of what I would already, so I'll just sum my thoughts with a quick nothing: it's the best DLC of any DLC in the subgenre

The level design in DLC is better then in the base game. The boss fights are more difficult, but has the same good quality, maybe even better. If you like challenge then it definitely worth it.