My favorite of the 7 movies, DD is my second because of the battles. In my opinion, having the movie taking place in an animated version of an actual city is a very original idea. Because of this, i tend to think more about the city more than usual. Also, the ending was sad at first, but near the credits, having you see the three pokemon(Latios(father), Latias(daughter), Latios(son)) kind of made you feel better knowing that everything was ok. Another thing, is that this was a severe sneak peak for the Hoenn series, because of two things, the pokemon in the pikachu short, and having Latios and Latias in the movie branched off, Master Quest(not yet in Hoenn, still in Johto). But thats what made it great. I myself enjoyed it and thought that Ash had a much LARGER role in this movie than in the previous, because you dont Misty or Brock as much as usual. I dont mind, actually you dont really care to notice anyway!
The one thing that i did not like, is that team rocket(Jesse, James and Meowth) were STILL in the movie. Thankfully they barely have any role. But it seems that in 4 and 5, team rocket members are the villains.

To say more, the music was great, the italian idea was great, the pokemon were great, the story was great, in bottom line, if i were to rate it... ***** 5 stars!