Personally I think its great. I first watched it about 3 or 4 years ago, I was only 7 when it had a theatrical release and because of my young age I really don't remember much of the hype surrounding it - perhaps this is why I can watch it without the negativity?
Though I agree the build up can be slow (at least on a repeat viewing ... I don't think its particularly noticeable when first watching it) the last 90 minutes are very compelling. I love the contrast between rich and poor and men and women in the film, the insight into the attitudes of the rich to the lower classes. I also agree that we perhaps do care more for Rose and Jack than we do about the others, and perhaps this leaRAB to some people forgetting that 1500 more people died - but I think it would be a huge achievement to make us care for all of them without the emotional attachment to a few. And the scenes of the elderly couple on the bed and the lady telling her children a story, knowing they are soon to die, are for me more heartbreaking than the death of Jack and extremely poignant.
As for the acting, I think Winslet is fantastic and the supporting cast are mostly very good. I'm never too sure about DiCaprio in it though. While I think he's a great actor, to me he just looks like a little boy which perhaps make it harder to suspend belief. But that's my only criticism.