A Dirge for Cascius is an intriguing murder-mystery/whodunit space opera set on a rich world, and following a scrutineer (aka, a detective) who breaks all tropes of how detective characters should behave. It is an interesting story, but it is not easy to read. If you're looking for those books meant to be re-read, this is it.
Let me start with the prose. In general, the prose doesn't get in the way of enjoying the story, but there are a few things to consider. First, Lott has crafted an incredibly rich world that is also filled with new concepts, each with custom names—and this is clear in the prose. Some elements can sometimes be only explained through jargon, and these are not spelled out; the reader is expected to infer these concepts from the text itself. Although I'm generally okay with this type of prose and approach to world-building, I do understand it may not be everyone's cup of tea.
Likewise (and this is a detail I loved), sometimes the metaphors/comparisons rely on in-book/lore-related elements. In general, once I grasped the concepts, these elements added to the immersion... but then again, it can make the book more difficult to read.
This is a third-person past-tense narrative in which we follow the protagonist, Cascius, making the narrator quite unreliable. Cascius is an opinionated character, and those opinions leak through the page—even when we can infer, through the other characters' gestures—that Cascius is woefully misunderstanding them. More often than not, he seems to do this on purpose.
Furthermore, using an lore-related device, Cascius is purposefully hiding information from himself, and (at the same time), seems to be in no rush to solve the whodunnit and prevent the next murder. This generates an interesting dynamic around the mystery-solving aspect of the story.
The "mystery/whodunnit" itself is handled in a nonconventional way. In general, purely mystery books aim to put the reader in the position of the detective, where they can deduct what's happening as the detective solves a mystery. I found that doing this in A Dirge for Cascius was almost impossible. In my opinion, the reason for this is world-building. Without spoilers, most of the "clues" to solve the mystery are intrinsically related to in-book concepts—and because there are so many concepts to learn, the intricacies do not pop up on a first read. I don't think it is feasible for a first-time reader to "foresee" the mystery or pick up the foreshadowing.
Something that intrigued me from the world-building itself is that this isn't purely sci-fi. Yes, there is a reliance on technology, space travel, and other "core" (to call it some way) things you could expect in a sci-fi book... but there are also other fantasy elements. For example, within the book, people understand the universe in quite a mystical way, and space-travel itself doesn't seem to be your traditional FTL/slipspace travel, but something that crosses between realms.
Finally, and going back to Cascius himself, I think it is worth nothing that he is majorly depressed through the book. We can see how his depression stains his perception of the world and of other characters, and how this changes as Cascius undergoes "cycles" of depression—alternating between allowing himself a bit of hope, only for it to last a few pages before he falls again in another depressive bout. It is difficult to read, because his struggle feels real. His behaviour may sound "inconsistent" to some reader, but I truly think it's a great depiction of those dreaded cycles.
TL;DR: This is a great blend of genres that fans of fantasy and sci-fi may enjoy; it breaks a lot of the classical tropes of murder mystery. It can be difficult to follow up due to the extensive worldbuilding, and I wouldn't recommend it as an entry-level book to the genre. Finally, if you're a compulsive re-reader like I am, this book is for you. I think you can only grasp all the nuances of A Dirge for Cascius through a few re-reads.