You guys should rly read something like Tramps Like Us or Otomen or something because imo, they're pretty good.
But while Ichigo doesn't have a lot of complexity, I'd argue the people around him do: Ishida was pretty much a loner from the beginning of the comic, and he wanted to prove that Quincies were just as good as Shinigami. But other than that desire to prove himself, he had no attachment to the other characters. Now he has a crush on Orihime and wants to protect her, and he seems to like Chad and Ichigo much more than he did when he was first introduced.
Rukia was also introduced as a somewhat violent to Ichigo but generally Yamato Nadeshiko personality to everyone else. She had a huge complex about killing Kaien, and I'd say that she still does, though she's managed to let it go. She also seemed to have shut herself off from most people during the first arc, and then she gets caught by Byakuya and Renji, and Ichigo and friends go to save her. Once this happens, she does seem to realize that all of these people do care for her, and she opens up to some of them a bit more, even encouraging Orihime when she felt upset because she couldn't fight Hollows. Once she defeats Aaroniero, she seems to have realized that she had no choice but to kill Kaien a while ago.
Orihime's really a roller coaster, who kind of went from being a joke character to being someone with a lot of angst because she didn't want to hurt anyone, and moreover just couldn't do it. She seems to have gotten the most attached to the group out of anyone, especially Ichigo.
...mebbe I should stop there because I feel internet backdraft coming on.