Most of this was one very long action sequence taking place over several locations as people kept chasing other people from one island to another.
The thing is, the whole "race to save AcE" thing was actually pretty well done, had the proper momentum and since of urgency, and actually managed to end with the epic stakes a lot of shounen tries for and doesn't succeed at. The problem is that, for about a dozen volumes, EVERY major character except for Luffy was MIA except for chapter pages. Ace had a small supporting role and Garp, Tashigi and Smoker had itty bitty roles, but aside from luffy, mostly of the characters running around were characters that didn't interest me, whether new or a previous antagonist who was showing up again. If everyone but Luffy hadn't been MIA, I may have felt differently about them, but as it was, my brain was just going "characters I don't care about keeping characters I do care about from showing up. (I mean, now that everyone is back, I am starting to like Jimbei...) So even though I intellectually appreciated everything going on, I felt "meh" a lot due to lack of emotional investment aside from the direct Luffy/Ace stuff.
I just would have rather gotten more of the crew in their various training than a lot of the other stuff, TBH. (Except for Sanji, because much as I like Sanji, Oda's issues with certain things were running rampant there.)
I do like the fishman island arc so far, though I don't have a lot to say about it. (And am trying hard not to think about the mechanics of fishperson mating, due to certain size aspects.) I also look forward to seeing how Sabo comes back into play (no body=no death) and to see if I start getting fandom's squee over Trafalgar Law. (Who I don't dislike, but have seen so much fandom squee over that the actual character was "oh...ok..." for me ,even though I know fandom's squee is after years of exposure.)
I do like the post-timeskip makeovers (Except for Franky's. He just looks extra weird now.) and am enjoying the current arc, though I don't have a lot to say about it.
Side note: I'm pretty sure OP is has the record for the most volumes I've ever read of a single manga series. I think both Bleach and Naruto lost me somewhere in the 30s, and Samurai Deeper Kyo would be the lonest series I've finished, but it wasn't quite 40 volumes total.