To be honest I'm not that worried about the dynamic between Thor and Loki, because it was such an acclaimed part of both "Thor's" and the "Avengers'" success that TPTB would never dare mess with it. The smaller details that I loved about the first film, though, are very much in danger. Like turning the futuristic Asgard into a medieval village, for example. Or the treatment of female characters. I'm worried I might end up hating the sequel because of things like that.