This reply contains mild Book spoilers up to Tiamat's Wrath, so don't read this unless you've read them.
We finished watching the season last night. I have to agree that it wasn't nearly as strong as previous seasons. Part of that was the nature of the material - splitting up the crew meant that if you're not equally invested in all of the Big Four then there are going to be stretches where you might start glancing at your watch. And for our household those stretches involved Naomi. And let's face it, if you're not a Naomi fan then Season Five is going to be a bad time.
And it's a shame, because I like Book Naomi. And we both liked early seasons Naomi. But the show's depiction of the Holden/Naomi relationship just hasn't worked for us. There's been more chemistry between Holden and Monica in a handful of episodes than in the entirety of the show's run so far and I think the producers realized that, which is why they brought her back to give Holden someone to play off of this season.
Regarding the Alex situation - I get why they did what they did, and I get why they did it how they did given the complexities of trying to adapt to the situation in the middle of a pandemic, but it still rankles. We're divided on who gets to be the new pilot of the Roci now. I'd like to see Bull stick around, but Clarissa is a qualified pilot as well...
The politics with Avasarala on the moon felt like filter, sadly. Mostly time spent maneuvering the character out of a position they didn't need to maneuver her into in the first place. (That and keeping her hands clean wrt Earth's escalation of the conflict with the Belt.)
Every scene with Amos was a treasure. Enough said.
Can we talk about Drummer of Borg? I like the character. I like the actress. But man, by this point she is an amalgamation of at least 3 book characters and the contortions needed to keep getting her into the right place for the new season are noticeable.
Finally, given the announcement of S6 being the last, I'm honestly surprised they chose to include as much of the Duarte/Laconia storyline as they did. Gives me hope that the rumors about concluding the story via film have some basis.