I finished the expansion probably less than week after the update was released, so it's been awhile, but overall, it was a mixed bag for me.
On the one hand, the levels look gorgeous, utilizing a mixture of old and new graphics to have its own look. The music helps compliment the presentation. I also liked the "new" weapons, even though it took me a little bit to realize that I always didn't have to charge the Calamity Blade all the way to get through some of the later areas.
On the other hand, and I'm pretty sure this has been talked about to death, but the difficulty. You can tell that several people worked on the level design because the difficulty is all over the place. The Coiled City, while it looks awesome, is such a chore to play through. Not TNT Evilution-tedious, but it just wasn't fun after awhile. Mind you, I was playing on Ultra Violence, so I expected it to be a challenge, but holy shit. Even Plutonia wasn't that tedious in most cases (At least its levels were shorter). Don't get my started on the last level. That section with all the Archviles almost ruined the whole experience for me.
Overall, I think it's a fine episode. I don't think it's as great as the original games, or even No Rest for the Living for that matter, but for a complete expansion, it's definitely refreshing coming from the older content.