I really liked this. It was a nice change of pace from the heavier political focus of
Vanguard and the 24th Century Pact era, and it did indeed feel "pulpy" - in the best possible way. It was a fast-moving adventure that was simply great fun, and there was a real joy for exploration and discovery, which gave it depth as well. The characters were fun, and it was nice to just get in there and tell an adventure story. A real out-on-the-frontier exploratory piece, with a 23rd Century edge that the more stately 24th Century exploration stories, e.g.
Titan, don't have. I think this series will fill its own niche in the lineup quite nicely.
As someone who likes having the Trek 'verse fleshed out wherever possible, I was pleased that we got further insight into the Arkenites and the Kaferians, two of the under-utilized allied species. Trek has so many established races that, really, we don't need to keep making new ones without cause, when there are already so many to choose from.
Speaking of the new race (for which there
was cause, naturally), the Tomol were a good addition to the setting. Their plight was very engaging; Nimur can hardly be called villainous for not wanting to give up her baby and then kill herself at 17, of course, and the whole matter is just so unfair that she can't help but be a protagonist as well as the villain. Nimur's arguments with Kerlo were also very good, because not only is everything Nimur saying reasonable (despite also often very wrong, sadly), but whether Kerlo's simple resistance to her arguments shows him to be truly noble or just sadly indoctrinated, as Nimur now sees him, is up to us to decide (it's both, really). "Yes, well done, Kerlo, you think everyone should die because it's for the greater good. Have a cookie, you good boy, you".

Nimur's frustration is again entirely understandable, even as she can't help but demonstrate through what she's become why Kerlo's right. This is common to Mack's work, though; one of the things I like about his books is his skill at creating situations that are difficult for everyone, that demand moral and practical decisions but don't have any easy answers. Which makes them primarily about character and how people respond to hard situations.
I felt sorry for the Priestess, Ysan.
I also really liked the character of Tormog, whose life is apparently one long theatrical sigh as he's pushed around, ignored and/or despised by everyone.

Please don't kill him!
I think this one's hard to grade, because it's a consistently positive experience and a great read, but the very fact that it delivers a fast-paced, engaging adventure so well means that it doesn't have the same impact as some other Trek books. So I'll say, for me it was Above Average, but if you ignore my preferences as a reader and judge it on what it was trying to do, I'd say it was Outstanding. A well-judged start to this new series, whether it's entirely your thing or not.
I look forward to seeing Captain Khatami and her crew getting the same attention as Terrell's people in the next book.