Its pretty amazing. It adds great features that feel like they belong, including a lot of great quality of life. The XUI is top-notch and should be reason for TFP to pause for reflection. (be a hero a post xui standalone)
Progression is slower but meaningful, and while some may complain its grindy, I found it lends to a greater sense of achievement that makes playing to day 50, 75, 100+ much more viable. The base game is boring by day 35 basically every time after the first. Multiplayer becomes the only way to redeem it. This was not the case with UL.