A lot of people seem to be upset with how Luke is depicted. He's now an angry, disillusioned grump living in exile. Supposedly that's out of character, but it's been decades since ROTJ and his life's work and students have either been destroyed or turned against him, so his turning into a grouchy hermit doesn't seem too strange.

Rey's parents turning out to just be drunks was a surprise (assuming Kylo Ren was telling the truth.) I was honestly expecting her to be either Luke's or Leia's child, but I don't have a problem with her parents being nobodies. I wouldn't be surprised, though, if Episode IX backtracks on this.

Snoke being killed this early was also a big surprise. I am disappointed that we didn't find out whether he's actually Darth Plagueis, but I think it's better that we remove him from the story early on or else Kylo's arc would play out too much like Darth Vader.