The game seems enjoyable from my limited play so far, with evocative character archetypes and options, and an array of advances, mutations and other developments which I can gleefully anticipate. The artwork is lively, high-quality and feels very appropriate to me. I found it fairly easy to create a character who felt different and interesting without being a bizarre departure from the premise, although I must admit I have a lot of exposure to 40K and have played this gameline before, which surely helps.
The core mechanics of the game are relatively straightforward and provide a reasonable balance between failure and success - it's a relatively gritty game, so a certain degree of failure is to be expected. This is particularly true of knowledge and technological skills (in the setting ignorance is a prized virtue and the world full of lies and secrets) and of social skills (virtually everyone is morally dubious, self-interested and deeply suspicious of basically everything).
Where combat comes into play, characters have a reasonable degree of survivability, but sensible preparation and tactical play are important to ensuring you can wreak havoc without dying. Here the skill system provides a good range of potential bonuses so those relatively low skills result in high rates of success. However, I must say it also gets really quite intricate and crunchy, and so is very much not for everyone. We spend a lot of time checking details.
The combat system is not simple, but there is satisfying weight to the game, with plenty of options in combat, aimed shots, a huge range of potential equipment, and of course, injury systems and a dramatic set of critical damage rules. I discovered my sniper could laser people so hard that their grenades exploded, on one occasion destroying the armoured vehicle they were standing on.
There's plenty of scope for variety and for power-development in the game, due to the disparity in equipment, which means a high-powered character can walk casually through low-powered gunfire without a scratch. This is highly appropriate for the setting, and also lets you demonstrate how far you've come (and makes very powerful adversaries both terrifying and an interesting challenge).
There are a large number of small changes from other 40K games, from the way certain weapons work to (more confusingly) the skill breakdowns, uses, and in extreme cases even which skills use which stats. Another shift is that now almost all skills can be used without specific training, whereas previous games in the line had a fairly even division between Basic and Non-Basic skills.
Where I have to ding this book is the editing, at least where the PDF is concerned. It is not the worst-edited RPG I've read (hello, Demon the Fallen), but I find it very hard to use. Some sections don't seem to be arranged in a very logical way - for example, the rules and reference table for obtaining equipment are 150 pages and 4 chapters away from the rules for that equipment - including all the keywords and details you need to cross-reference!
The bookmarking is fairly plentiful but sometimes seems erratic, as well as being a random mixture of all-caps and sentence case, which is just untidy. I was not able to find rules for Cover, for example (neither by bookmarking nor in the index), which seems a pretty basic topic.
The search function seems extremely poor, and although I can't check, my impression is that the book has not been adequately set for text searching. As a basic example: searching for "maglev" will highlight "Ferric Lure Implants" (or rather, "ure Impl") on p65, although in this case it is at least quite near to the world "maglev". This makes it frustrating to use, given that this is quite a complex game with a lot of specific powers, abilities and jargon, and the aforesaid slightly suboptimal ordering. There are also some cross-references and links that are simply incorrect: the Noxious Discharge weapon modifier references "see page 243 for rules on Smoke" but there are no such rules there. I think they may mean the brief reference on page p245, but it's shorter than expected so I'm not sure.
There are also so very many tables to reference regularly in play that I really feel like there should be a single extra appendix at the end which simply includes all the tables. It's a PDF, after all - no space issues really, and it would be extremely helpful for keeping things moving smoothly at the table. Or it could be an extra download. I expect to make one myself when I have time.
Unfortunately the usability issues for this PDF (and to a lesser extent the game as a whole) are severe enough that I can't rate it as highly as the content and presentation deserves. When a game is this long and complicated, ease of use and high-quality indexing/referencing are crucial. I like crunchy games, but I want to know I'm playing them right. If they release an updated PDF that fixes these issues, I will adjust my rating.