Yeah, I felt that way too. I might even say it's one of my least favourites, of all the episodes I've seen so far, although that's probably more just because of the expectations one has going into it. It's definitely pretty disappointing as a series finale.
Miyazaki's other red jacket episode was great-- I'd almost rather that it were switched so that "Albatross Wings of Death" was the final episode, and "Aloha Lupin" was #145. The Albatross one doesn't really feel any more like a 'final' episode, but at least it's really fun, which is more than I can say for "Aloha Lupin".