As a player, I love this book. I find it kinda difficult to tell when a book is meant for the player as oppose to the GM but Rites of Battle is easily one of the best player-centric books for Deathwatch. The expanded chapters, the new equipment, the advanced specialties, new psychic powers all cater to being a better Space Marine. Obviously, if you're a GM, you'll want this so you know what your players are doing. The quality is great and I have no complaints there.
The biggest gripe I have with this, which is why I rated 4/5, is that the bookmarking is TERRIBLE. It's just a giant list with no collapsible categories and and a lot of section names in all caps. It's not fun to scroll through and it's a huge peeve of mine having it like that. I hope this can be resolved somehow by DTRPG or FFG.
[4 of 5 Stars!]