It was nice to revisiting that world, the characters and the lore surrounding them. Plot was decent, if a little shonen-esque, while giving new incite into things relative to the present plot and beyond. Presentation was great, though the occasional jittering of the animation at times irked me. Music was excellent.The final boss was quite the spectacle to behold. All around, it was a satisfying conclusion.
However, while I enjoyed Vol. 4, I'm glad I decided to play it first instead of waiting. Vol. 4 locked us out of features the entire campaign and part of the immersion in these games come from those features and the sense of progression and accomplishment you get from building up your Haseo in level and gear. If I'd done it the way I'd planned, I'd probably feel the loss of those features a lot more, since I would have spent time building them up.
I wasn't quite in my groove either until partway through Vol 1, so it'll probably feel a lot better playing it again after replaying the other Volumes.