PS - I didn't know it was Miyazaki's debut film before watching, but looking back, I can definitely see his style.
The country, the architecture, the castle are all just so beautifully drawn. The fight scenes are incredibly fluid and energetic. It was made in 1979 and so, there are a couple of tropes that haven't aged well - specially the Damsel in Distress, but other than that, the plot is solid. The female characters, when they're present, aren't overly sexualized. It's just a very well made film. Above all, it's just so fun! The chase scenes are freaking hilarious. The villain is plain evil so you don't have to think about any morally gray areas or whatever. Just sit back, relax, laugh and have a good time.
Highly recommended.
The TV Series is based on the original novel, isn't it? I thought at first it was an adaptation of Lupin III.
Kinda, Lupin III's author, Monkey Punch wrote a gentlemen-thief manga series of a descendant of Maurice Leblanc's Arsene Lupin, though Leblanc's Lupin is largely separate from Monkey Punch's Lupin. The best comparison I can make for the Green, Red, and Pink Jacket Lupin series (the different adaptations of Lupin have him wearing different colored jackets) would be a heist-of-the-week Simpsons: canon and character backgrounds change or are irrelevant and characterization differs between episodes and series.