I have little tolerance for absurdly prolonged series (in any genre), so for years I put off giving Jojo no Kimyou na Bouken a try. Luckily, I realized my mistake while reading another of Araki Hirohiko's works -- Under Execution Under Jailbreak -- which opened my eyes to the extent of the mangaka's writing prowess.
Part 1 - Phantom Blood - While this is my least favourite instalment of the Jojo saga, it's still better than most mainstream shounen action series. The course of events tended towards being somewhat predictable, but the ending was thoroughly unexpected; a much more fitting conclusion than the one I'd predicted.
Part 2 - Battle Tendency - This is where strategic thinking really begins to come into play during the battles - a feature which continues in all the sequels. It's better than part 1, but still the second-to-last in of quality (of plot, characters and art).
Part 3 - Stardust Crusaders - From here on out, Araki Hirohiko's brilliance really begins to shine. The special abilities (Stands) and the outcomes of the fights become entirely unpredictable, and the characters are much more endearing. Jotaru Kujo as the protagonist is a marked improvement on the more old-school type Jonathan and Joseph. The art has improved, and the mangaka shows definite signs of having learned how to better convey action sequences as well as subtler details such as facial features and expressions, despite retaining his trademark style of weirdly-drawn bodies.
Part 4 - Diamond wa Kudakenai - The draw in this series lies in that it deviates from the formula followed by its predecessors. Josuke and his friends are not under direct threat from Diego Brando, and focus their energy towards battling opponents on a much smaller scale. The drama and tragedy which characterized the earlier instalments is virtually non-existent, making it more fun (and childish) than any other part of the saga.
Part 5 - Vento Aureo - I refrained from reading this, as the scanlators of Steel Ball Run (JoJo Project) have cautioned that the translations on the 'net are (despite their apparently good quality) grossly incorrect in several crucial places. No alternative is currently available, though.
Part 6 - Stone Ocean - The elitist "real fans" are fond of claiming that the series went downhill in this season, but I disagree. Stone Ocean is one of the most interesting, insane and unpredictable instalment to date, and I do not recommend missing out on it. The stands are bizarre, as are their s; the prison setting and strong female protagonist (Jolyne is a great character -- every bit as awesome as any male JoJo) make for a refreshing new angle, and the mind-boggling conclusion was something I enjoyed very much.
Part 7 - Steel Ball Run - Gyro Zeppeli's presence as a protagonist alongside Johnny Joestar is a welcome improvement, and imo he's one of the top 3 JJBA MC's so far.
I was actually pretty shattered when he died, and I don't usually care much about character death. He and Johnny also make an excellent team, beating out Jolyne and Hermes as my favourite JoJo fighting duo to date. The plot is creativity itself, strangeness and all, making this probably my favourite instalment so far (though it has tough competition). The art is pretty weird in that the bodies/poses are still bizarre, but the faces of some of the characters (both male and female) are oddly beautiful. (Jojolion is the same, though not parts 1-6: perhaps Araki Hirohiko decided to update his art style together with the series reboot that came at the end of Stone Ocean)
Part 8 - Jojolion - Waiting on further scanlations, but from what I've seen, the romance aspect of this one is a bit annoying. Stone Ocean is the only preceding season which featured a clear pairing, and both Jolyne and her boyfriend were interesting and likeable characters (so I had no worries going into Jojolion), but Yasuho and Josuke are irritating as no other pair of JoJo MC's has been so far. Oh, well. Only time will tell, I suppose. Plot-wise, on the other hand, it's just as satisfactory as its predecessors.
Despite my gushing praise, I'm not surprised that very few people actually like Jojo no Kimyou na Bouken -- despite being a long-running battle manga, it's pretty much the definition "non-mainstream." If I were to recommend it to anyone, they must be: (1) someone looking for something different from the typical action shounen/seinen (and that includes overt romance, ecchi/sex, school life, and in-your-face comedy), and (2) with a high tolerance threshold for weirdness. If you don't possess one or other of those qualities, this isn't for you. But don't be daunted by the volume count -- I guarantee you'll barely feel it: in 111 volumes (as of the time of this comment), the plotlines, the characters, the Stands, the battle strategies, and the humour have yet to become stale, flat, cliché or repetitive.
