I actually really like the love story in Titanic. The world doesn't hate Titanic as much as the Internet would lead you to believe.
When I first saw the movie as a kid, I didn't care if the story was a bit ham-handed and un-subtle. Now that I'm almost a decade older than Jack and Rose, I can forgive the un-subtlety of the story because Jack and Rose are actually just kids, something that obviously never occurred to nine-year-old me.
Overall I just find the love story simple and grand and sweet and to-the-point.
I have a friend that loves Before Sunrise and tries to convince me that it is better than Titanic.
For me, Before Sunrise wasn't BAD really, but it had far less depth for me.
These two people just met today, and sure they get along really well, but there's no real romance beyond that, as well as a large portion of the attraction being more sexually based. It comes off as a slightly more romantic one night stand, in my opinion. Jack and Rose have build up.
But Before Sunset? Now you learn that these two people have been on each others minds for years. That it wasn't JUST a one night stand, that it ACTUALLY meant something significant to these two people. And there's a lot less emphasis on the sexual attraction. Instead of feeling like "these two really want to bang" like I did in the first, you feel like these two are the best friends in the world, and truly have something special with each other, legitimate care and love.
In that way, it almost enhances Sunrise if you think of it as a trilogy instead of individual films, but that's not how I'm analyzing this.