I'm nearing the end of act III with a couple of friends and I'm having a great time. I'm very likely to have a 2nd and maybe 3rd playthrough coming up. I love the game as it is, but I do have a few complaints.
My biggest complaint is that we can't just let a more appropriate character take over a conversation. One of my clumsy, dim-witted brawler friends runs ahead by one pixel triggering a cutscene, and I can't jump in mid-conversation to smooth things over with my bardic talent. This is our most common reason for loading a previous save.
Second biggest complaint is the number of things that you can mis-click to destroy your character's reputation. I'd love to be able to opt-in to an "are you sure" dialog when you accidentally click a random item on the floor while moving around. This is our second most common reason for loading a previous save.
Absolutely loving the game despite some very confusing storyline elements that must have relied on earlier foundational elements that we missed.