Expert mode is insanely hard, especially the first day ingame, but the rewards are so good. I've been playing with a small group of friends and it quickly became clear that we had to start utilizing most of our various resources that we didn't use to, like grenades and lower tier items we used to skip just to survive.
Also, as typical of the game, many of the new items are hilarious/referencing things like JoJo's Bizarre Adventure, which is cool.
Edit: Typos are the bane of my existence