Aliens has far, far better characterization with Ripley than any aspect of Titanic imo. Just because it didn't make people sob doesn't mean it's any less powerful in terms of creating a human character on screen.
I can understand what people like about Titanic, but for me it's where Cameron lost his spark. He'll always have his technical genius, but he lost his powerful characters here.
You can't create that type of emotion in an audience if they don't care about the characters.
The strength of his work on Titanic and Avatar beyond that is IMO you *feel* like you've gone to a different place for 2-3 hours. In Titanic you feel like you've been on that ship, you can almost smell the fresh paint. In Avatar you really feel at times like you are on Pandora. This is something I don't think many filmmakers can do.
I think he's taken that aspect of his filmmaking to another level.
Ripley is cool but she was also a pre-existing character, I like his Linda Hamilton character arc in T2 moreso to be honest.