These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Broken Base: Sort of. Cagliostro's glaring difference in tone compared to other anime entries have fans either decry it as a disgrace to its source material or embrace it as being all-round enjoyable. Some fans have explained it thus: "Cagliostro is a great movie, but a bad Lupin movie."
Contested Sequel: Though not being much of a sequel (since Lupin III runs on zero continuity), Miyazaki explicitly sets this film toward the end of Lupin's career, meaning it takes place after Mamo. Even fans who like both movies prefer not to think about them at the same time.
Fridge Logic: Lupin has his Walther P-38 pistol melted into slag by lasers in one sequence. One can only wonder how the heat didn't cook off the ammunition in the magazine or fuse the metal into his hand.
Germans Love David Hasselhoff: The movie was a failure on its initial release in Japan for being too cartoony and not having Lupin's adult humor. By contrast, Americans loved it and it's more well-known and sold far better than "Red Jacket" or Mamo. Two things can explain why — First, very little Lupin had made it to the states by then, so Cagliostro was the largest release at the time – many American anime fans were introduced to Lupin with this film. The other reason is that Streamline and Manga marketed it as a Hayao Miyazaki film, so viewers go in expecting something Miyazaki-like (which they will get).
Moe: Princess Clarisse is popular among fans, was featured in early fanworks and doujinshi, and sometimes even said to be the first "moë" character.
Misaimed Fandom: Princess Clarisse was not intended to be the Trope Codifier for moë. Miyazaki despises that trope. As a self-avowed feminist, he thinks the concept of moë is a terrible fetish that devalues girls.
Vindicated by History: When Miyazaki made this movie, he put his own spin on the Lupin character, toning him down from the raunchier, more manic version depicted in the manga and animated series (apart from the first series, which was also somewhat toned-down since he and Takahata were the showrunners for about 2/3 of it). As a result, it flopped in Japan when it was first released – the people who liked Lupin for what it was were turned off, and the people who didn't like Lupin didn't have any reason to watch the movie since no one in 1979 had heard of Hayao Miyazaki. It was only years later, when Miyazaki gained recognition for his original works with Studio Ghibli, and more people watched the movie without any prior Lupin experience, that it belatedly gained a reputation as a classic. Other animators in both Japan and America liked it and would Shout-Out to it, which drew people in to discover what was being (often subtly) referenced.