The objective side of me liked several aspects of Abaddon's Gate: it was a continuation of the main "super powerful aliens" storyline of the Expanse series, it had many fast adrenaline-filled moments, it was logically sound, and it was very quotable. Plus, it reached a good point in the overall arc of the series.
But the subjective side of me missed Bobbie and Avasarala. I could not see any reason for completely omitting the two best characters of the Expanse series in the book 3. And I didn't manage to bond as well with the new characters, with the exception of Bull.
In particular, I found Melba's story to be uninteresting. Usually I am a great fan of redemption arcs, but somehow Melba's journey felt predictable and contrived form the start, and because of that her chapters felt tedious to me. I kept thinking: "I know where this is going".
And even overall, I found Abaddon's gate to be predictable. As soon as the purpose of the Ring was established and the new characters were in place, I guessed the ending in good detail. This can be a plus or a minus for different readers. I usually find predictability to be a minus.