Titanic has a very uneventful story construction, apart from using a standard flashback technique everything is pretty much by the rule - I wasn't surprised by any of the story turns. Billy Zane's character could have been a bit more ambivalent, but in the 90s the one-dimensional character of the major opponent might still be OK. I strongly believe that audiences (also the young ones) have matured thanks to information technology, and are quite aware of the conflicting motivations that make somebody "evil" in the moral sense.
The most interesting part was the audience reaction. There was quite a bit of laughter at some scenes that were not intended to produce any, or worse, were meant to feel solemn. Most of the people in the cinema felt a bit bored at the lengthy middle part, and there was quite a bit of muttering. (Sat night couples crowd). The experience should have been sped up and more opportunities to showcase the 3D might have come in handy - maybe even a re-editing for some of the smaller subplots might have helped enormously.
DiCaprio drew most of the giggles. Looking back from now, his "lover" character seems way too childish and young for the more mature Winslet. If he'd acted this role today, DiCaprio might not only have the right looks, but also the right "dark" side to his backstory that might lend more credibility to the romance.