Hello, after getting Rites of Battle late and having to do some other stuff before reading it in full here is now the complete, uninteresting and late list of what I think about it.
Chapter I:
Trials of the Aspirant:Interesting fluff and ideas. It actually made me think about what exactly my chapter does to keep potential traitors and other liabilities out of the chapter.
Birth of the Chapter; For me, this was supposed to be the heart and soul of the whole book. Unfortunately the book is a Pariah. Almost everything is fluff and random tables for people who can't decide for themselves. Not only that, the rules are also incomplete (no rules for 4 First Founding chapters) and illogical (chapters with pure gene-seed follow all the rules of their progenitor chapter, seems the Black Templars are corrupted beyond repair). Codex Demeanours made my heart jump for a moment. I recognized a lot of names from the chapter customization rules of the 4th edition Codex. Unfortunately it's only Demeanours. Gene-seed deficiency was one of the good parts. Chapter flaws was tied to the purity of the gene-seed and again something that has nothing to do with it. Dark Angels practically have "We Stand Alone", Black Templars have Faith in Suspicion" etc. Then there was some interesting fluff to consider. Combat doctrine was the worst for me. My chapter would have used "Stealth". "Some of these chapters utilise subtle modifications to armour and weaponry, shielding them from detection until the very last moment." Hello? This is vital for the Demeanor See, But don't be Seen and the Stealth combat doctrine (unless you make a chapter of scouts) and it gets handled in a line of fluff text? There need to be RULES for that kind of stuff. The solo and squad abilities are nice but by far not enough. The Advancement tables are a lot shorter than those of standard chapters, but since there are so many advancement tables in Deathwatch I can live with that. However, the chapter tables should be bound to combat doctrine and be less random. Why do you hate Eldar if you prefer to kill enemies from afar? And yes, it says everywhere that I can talk with my GM to make stuff up. But that's something I don't buy a book for.
The new chapters are nice, but I think some new chapters should have been left out in favour of the missing first foundings.
Chapter II:
The Call of War: Chapter Deeds are limited to very few chapters, but the list is generally short, so it doesn't matter as much. All deeds are interesting to give you character a little bit of extra depth. The same is true for distinctions.
Now the Advanced Specialties are in my opinion the second-best part of the book. The only thing that annoys me a bit is the part about it normally not being possible to get two. It's entirely possible for a first company veteran to become a champion and later a captain, at least in normal chapters some people will maybe want to play. That can lead to some redundancies with issued gear, otherwise there should be no problems to ignore it. The Specialties themselves are great. Only the Kill-Marine is again someone who is fluff-wise supposed to be stealthy but has no way to effectively sneak in power armour. This time there is even something in the text about them "often" not using power armour and Astartes weapons and scout sergeants being the best kill-marines. I guess this is meant to balance them with the characters from Dark Heresy and Rogue Trader but doesn't seem right. Still this advancement is absolutely vital for single cross-over marines because it allows them entering squad mode while solo.
Chapter III:
Expanded Wargear. This is the best part of the book for me. A whole bunch of new mean, brutal weapons to show chaos marines and Tyranids why messing with the MIB is a bad idea, new tools, and new relics, among them a special auspex the Deathwatch "borrowed" from the Grey Knights.
And the best: Rules for all Marks of Armour from I to VIII and new history tables. I could spend hours with them.
Chapter IV:
Vehicles: A very important chapter that allows for a lot of additional challenges in missions. Nice to see that the Stormraven is in there, without picture,
However, some things like allowing a kill-team to requisition a Land Raider seem a bit weird. Tank combat is pretty much the exact opposite to kill-team tactics.
Chapter V:
I love the new rules for renown, the descriptions of honours (nice to know what's the meaning of all these things in a space marine sprue. The additional assets kill-teams can requisition are great too.
Chapter VI: This chapter makes Watch Fortress Erioch a living place instead of just a something you return to between missions. You can even have real adventures set entirely there. The NPCs are interesting, some where seemingly made before the Specialties were finished, there's an Apothecary kill-marine. What I would have also liked a lot would have been a bit more on the things NPC would be willing to do to achieve his goals. Inquisitor Ghraile for example is willing to free the Tyranids on Erioch to show her colleagues how dangerous they are. That's kind of moronic but it shows pretty clearly what she's willing to do. Watch Captain Ramiel on the other hand has been in the Deathwatch for decades to spy after Black Shields and find out if they're Fallen Angels. But what would he be willing to do if he finds one? He can't denounce him to the Watch Commander without betraying the secret shame of his chapter to the Deathwatch. And he can't kill or kidnap him without betraying the Deathwatch, which would probably be unpleasant when found out...