If you loved Legend of the Millennium Dragon, try Naruto the Movie: Legend of the Stone of Gelel
A bridge between a film you've already seen and one most people haven't. Here's what they share, and what the second one does that the first one doesn't.
You already loved

Legend of the Millennium Dragon
→
Try this next

Naruto the Movie: Legend of the Stone of Gelel
What they share
Both films are directed by Hirotsugu Kawasaki, and they sit in Adventure / Animation / Fantasy territory. If that's the register that drew you to Legend of the Millennium Dragon, the second film will land in a comparable space — through a different lens.
What Naruto the Movie: Legend of the Stone of Gelel is
Naruto without a leash. While on a simple search-and-rescue, Naruto, Sakura, and Shikamaru are ambushed by Temujin, a knight in search of a powerful artifact. The three ninja are separated, leading Naruto to wonder about Temujin's motives. A nice, self-contained adventure for fans of the series.