Overall, it looks pretty cool, and, for beginers, either in RPG or in Warhammer40K, this should be amazing, however, I believe it does need suplements to achieve it's tru potential.
Adeptus Astartes marines, for example, have a single class, and though the game recomends you customize it for SM specific games, so you can have Assault Squads, Tactical Squads, Devastator Squads etc, you would need to create such systems yourself.
I believe it is a fair trade off considering you can play pretty much any kind of campaing with this system, customize a few classes for more in-focus campaings (Space Marines only, for example) doesn't sound like a problem to me, but, given it's competition is Death Watch, Rogue Trader, Dark Heresy etc, I believe this game would do well to release supplements for this kind of more focused games.
It DOES say in character creation that future supplements may bring new classes (even new races, given only humans, orks and eldars are presented in the book), but so said the previous edition also, and that one released 2 pre made missions and died out.
The second edition is published under a new company (well, cubicle 7 isn't new, but it wasn't the publisher of first edition), and I hope this will lunch off this time, but it does need suplements to reach it's true potential. Or, you know, you can play a few games, get the felling for it, and make your own custom Tau, Necrons, Tyranids etc.
Buying this game you get both 1st (Legacy Files) and 2nd (all the rest) editions, so you can also compare each other and use whichever rules you find best. I'm certainly mixing a few things to better suit my taste.
ps: if they start releasing supplements later on, I'm increasing the rating, but since I believe it requires supplements and the previous publisher promissed, but did not delieve on it, I'm not giving the benefit of doubt this time.
ps2: I had bought the digital copy of the first edition last month (March 2020) in this site, and only later discovered a second edition was about to be released. I wasn't quite pleased with paying for something about to go obsolete (not angry, because I should have checked it before buying, but certainly not pleased). Yet, upon release of this edition, I got it's digital copy for free. This may have biased my rating, but hey... if the new publishers want to please the disapointed buyers of the previous publisher, I see that as a plus.