Farewell to Nostradamus was actually my first exposure to Lupin (the fansub I watched called it 'Die Nostradamus Die', which I sort of prefer just for the B-movie quality) and I recently rented it again and I really enjoyed it.
Lupin is one of the rare shows whose dub I actually like, both of the dubs, actually. I can watch it either way and be perfectly happy, which literally never happens with anime.
Harmonia's Treasure is one of my least favorite of the Lupin ventures, there were only two things I enjoyed about it. I also really didn't care for Secret of the Twilight Gemini and that more recent one whose name escapes me, the one in Greece with the harmonics stuff. Yeeaaaah.
But yeah, Lupin's up there as one of my long-term standbys of things I enjoyed in the day and still consistently enjoy now, which is a depressingly short list. I need to get more manga, Monkey Punch makes me laugh.