I would say it's mixed. It's not the series that I enjoyed the most but did get some enjoyment. When I first watched Part 5, felt like the series was a bit "dry", that was down to the voice acting deliveries in the Italian dub despite the cast doing their best. This was during the time when there was no English dub of the series. Thought that the English dub would improve, it did a bit but not as expected. (This is no way to bash the voice actors at all because they all did a fine job, it was just a first impression of the series)
Character wise. Did feel that Lupin felt a bit invincible especially by the end (just the last episode, the others were more in line even if in the series flip flops between more early Part 1 and the more typical Lupin, again fine by me). Both Albert and Yata have been great additions to the series especially Albert with his motives, connection to Lupin and would have been good as a rival in its own right. As for Ami, it just didn't feel right. A teenage girl having a "dark and disturbing" background and wants to be with Lupin, not in the typical way of girl of the week either... Wasn't keen on her being the main focus (again) on the 3rd arc. It also in a low key way reminded me of another character called Ami who was also considered an asocial genius from another series. A case of anime being influenced by anime or manga and not just Episode 12 with the cosplayers.
The big issue personally was that Zenigata was rather underused, even in the Part 2 inspired episode him not being there didn't feel right. Episode 4 was basically the highlight for him in the series as well as the last bit in Episode 5 and Zenigata, Gentleman Thief. Only thing that I can think of was that Koichi Yamadera was too busy with other stuff, rather like why Goro Naya didn't get much in the later 2000s TV Specials due to his health.
Outside of a few moments, wasn't keen on Fujiko in this series. Also why would Fujiko spend a couple of episodes in a cage and don't seem too bothered about it?
Animation wise it's good for a modern anime. I did feel that it got rushed towards the end with either episode 22 or 23 being the worst in the series with some off modelling and more static shots of the characters. That was pretty jarring.
The idea of arcs were at least implemented better (just by comparison) than Parts 4 and 6, they felt like they could be mini TV Specials with a bit of work. Just on the grounds that the storyline episodes were put together as a block and not spread out. Had the second arc been a TV Special or an OVA, it would have got a decent ranking. As for the standalone episodes, in many cases enjoyed them more than the main series itself. Episodes 6, 11 had character interaction with the main cast that most of the story episodes didn't have (sometimes you get Lupin and Jigen or Lupin, Jigen and Goemon with an iffy issue but nothing like Part 2 or some of Part 1 even), it had a level of experimentation. Haven't seen Fujiko's Gift since the original Italian airing so have to re-watch that one since I didn't really enjoy it the first time around...
Outside of the standalones though, it's the case of re-watching an episode or even parts of an episode out of enjoyment but there are some episodes that probably wouldn't watch again (3rd arc). Meaning that as a story based series in most cases won't watch the entire arc due to not enjoying episodes.
There were some writing issues (the mentioned iffy issue, the rushed ending with Ami and Enzo, a bit animesque in places) but did also have some well written episodes with some great lines, jokes and expected tone (either light hearted or serious, even both). Pacing felt good especially for an modern anime where it is expected to have static scenes due to budget, timing and animation concerns (outside of either 22 or 23 where it WAS more in line) yet Part 5 felt brisk.
Speaking of which... Another issue that I felt (and similar one to Part 6 and Goodbye Partner with its misleading advertising), Part 5 was advertised to be set in France. Unlike Part 4 where it took advantage of the Italian setting, the France setting was barely there. It could have been really any similar country, even fictional like some of Part 5 itself. It also meant a bunch of missing opportunities in this series (especially with Arsène Lupin). It says something when a few Part 2 episodes and even a Part 3 episode felt a bit more into the setting than most of Part 5.
Then there are the "picky little details" that aren't a big issue but annoy a little. While I did really like Episode 6, it felt like a Part 2 episode (one that had the Yuzo Aoki and Yoshio Urasawa duo) rather than a Part 3 one where the irony that the next episode felt a bit more in line especially with betrayals. As mentioned in the deliveries, the Part 2 and 3 inspired episodes didn't get that expected hit in both the Italian and English dubs. The fan service (as in the multiple references, not as in Fujiko type of fan service) got a bit much in places. Not enough to go ugh... though.