Leo and Kate were each excellent, though I thought that they looked mismatched; he looked like he was twelve in a couple of the scenes and she looked like she was in her mid twenties. His looking like a tween was actually distracting at times, but under repeated viewing, Leo's performance holds up pretty well.

If I were going to make a casting change, I would have recast Jack. Everything else I would have left alone.

Chris O'Donnell in the role of Jack would have been very similar to Leo, but he would have looked better across from Kate.

On the other hand, I would have loved to have seen Val Kilmer as Jack. It would have been a very different Jack Dawson, but Kilmer could have brought a lot of depth to the character.

Daniel