My biggest disappointment was definitely the love triangle and how all characters involved in that were handled. As a side note, I overall felt that OB had way too much bloat, too many Bridge 4 chapters that served as nothing but worldbuilding/characterization filler where we instead missed out on a lot of important moments (such as Jasnah and Navani's reunion, and Navani's grief over Elhokar). In general it was just lacking focus and going around in circles, especially in regards to Shallan's arc, and Dalinar's Blackthorn flashbacks became a little repetitive too (but I've never been the big action reader lol!).
But going back to my original point, the romance arc was a huge let down. Not so much because of whatever I shipped (I actually really liked Shadolin at the end of WoR), but it felt like the love triangle cheapened the characters; Kaladin was treated like a plot device, Adolin lacked any depth and internal conflict, and I'm especially unhappy with Shallan's decision at the end, as it feels too much like a statement that a woman--and a mentally ill one at that--needs a man to be happy and fix her. The healthy choice would've been for her to step back and take some time for herself, and I really wish that's what she would have done.
Naturally the series isn't over, and Brandon might have had an intention behind getting Shallan into a marriage while she's still very much in an unhealthy mindset; I just hope this is addressed in the next book, because otherwise I'll unfortunately have to declare myself pretty unimpressed with this female representation.