Kamurai
Decent watch, probably won't watch again, but can recommend, especially if you're a fan of the series.
This movie is much less about the "main" couple, and instead uses them as more of a setting for an international affair that happens to be around Christmas, and happens to be around the time she's going to have a baby.
While the story itself is clever and a decent basis for a movie, it gets a little hamstrung from being shoe-horned into this movie. Instead of being a clever Scooby Doo movie, it's a so-so Christmas movie.
Still, it retains the charm of the previous movies, and is a decent watch, even if it's not a great movie.