4 movies in and a distinct formula is definitely starting to set in. Structurally, this film is extremely similar to the previous film (which I had plenty of issues at the time - read that review for more details), with the gang proposing a trip followed by an hour or so of light adventure before the sudden reveal of a hidden society two thirds through culminating in a major battle at the end. Unfortunately this time around I found the ocean exploration to be rather dull, slow and boring. Some minor tension is introduced at a few points thanks to encounters with unknown creatures andthe power of their talking buggy, however it is otherwise a slog to get through. The latter portion of the movie was also a relative let down with the underwater society being bland and only a single new character being introduced who himself was totally unremarkable. While the film does offer a slight degree of educational value for children, such as the explanation of evolution and information on the Bermuda Triangle, it still does not deliver enough to be worth a watch in that regard. If anything, kids too would likely get tired of the dragged out underwater exploration. The animation and sound is also nothing special, with its age obviously showing and even being subpar compared to other Doraemon films from the time. Overall, Doraemon the Movie: Nobita and the Castle of the Undersea Devil is the weakest movie in the franchise thus far, having a slow and dull plot, uninteresting new characters and locations and relatively poor animation.