The Fuma Conspiracy (why do I often think of this as "Plot of the Fuma Clan"? It's never had an English release by that title, has it?)
As we all know, it's pretty great. Very smooth, film-quality animation, it's nice to see Goemon get some focus for once, Murasaki was a cool character. I really liked the tough, competent, patriotic Zenigata, and the badass and athletic Fujiko. Without a doubt, though, the best part of the movie were the chase scenes. The ones in Mamo, Cagliostro, and Jigen's Gravestone were all great, but this one beats them in just how completely, hilariously nuts it gets (the poor schmuck in the bathhouse with the Fiat right at his heels never fails to get a laugh out of me).
I also really dug the rural setting for most of the movie. Lots of lovely mountains and forests (reminds me a lot of the areas in my native Kentucky where some of my family lives, as odd as that probably sounds). Lots of great comedic moments, from the chase scenes or Jigen trying to fire his Magnum before realizing it's not there. I also liked the nods to earlier entries, like Lupin's face changing to his older character designs, or Murasaki wearing Lupin's red jacket. And "Don't Say C'est la vie" is a really catchy song, despite not being a Yuji Ohno jam.
As far as downsides go, the Fuma themselves were cool, but their leader was bland. No personality at all (ah well, not all the villains can be as memorable as Mamo). The music was ill-fitting, too. It wasn't that it was bad (again, that opening theme was great. I've listened to it at least five times since I started writing this post) , but it really didn't work for the franchise or this particular story. And the dub...well, it's not great. Lupin's Rupan's voice is too nerdy and nasally and Jigen almost sounds like something out of an Abridged Series parody.
As a footnote, I like to think that this one is set around the same time as Cagliostro, near the end of Lupin's career. Not only are the character designs similar, but there's also a sense that things are winding down in general. Fujiko doesn't rely much on her sexiness here (maybe because she's getting older? Her being afraid of aging is a pretty consistent character trait), Goemon tries to settle down and get married. Lupin was willing to fake his death, which caused Zenigata to retire. None of it sticks by the end of the movie, but nevertheless...