Part III features a shocking pink jacket! Now this is easily the least popular series, and for quite a while was rather unfairly written off – but with newer releases cleaning up subtitles and visuals it's been seeing a reevaluation in recent years. And as a fan of it myself hopefully I can encourage you to give it a look!
Director Yuzo Aoki compared his approach to Neapolitan ice cream: using three "flavors" of Lupin – hard, soft, and comical – mixed in different proportion to explore the character. Visual variety was embraced as well – directors and even animators for individual episodes were given freedom to interpret the model sheets, shifting the cast from square-jawed handsome men to squiggly looney tunes – resulting in bright, bold episodes that are really fun in motion.
If III does have a weakness, it's that it overall is "good not great" – despite its visuals, storylines are often more grounded than Part II, and although consistently enjoyable there aren't many standout all-timer episodes. This does make it great candidate to watch a little here and there – you might just like its style!
Though popular enough to get its episode order extended from 26 to 52, its popularity began to falter near the end (often preempted by baseball games) and was ultimately cut short to 50 episodes without a true finale. After III concluded, the franchise would shift to television specials for decades instead of ongoing series.
If you're a weirdo like me who enjoys Seijun Suzuki, check out episode 13.
"Lupin's Lost Jacket: The Story Behind Lupin the Third: Part III", Discotek Lupin the 3rd Part III Blu-ray liner notes (2021)
"Lupin III Part 3", Anipages (2012)
"The Forgotten Lupin III Interviews – Yuzo Aoki", Wave Motion Cannon (1983-1999)