I just wanna say that this game is good, really good.
It doesn't have the most fun mechanic from Warhammer 40k Sanctus Reach, the free overwatch, but everything else is better. The army building is miles better with an actual incentive to keep units alive, the combat is better with more activatable abilities and more assymetrical units leading to more mixed up play patters, the UI is miles ahead, the campaign is incomparably better with no padded out trash fights, hell even the cleanup phase where you need to kill remaining stragglers is more fun.
Given that I already liked Sanctus Reach this is a homerun, I consider this the best Wh40k squad tactics on steam at the moment.
Yeah it has some usual Games Workshop retardiation. There is only a space marine campaign, and the space marine faction is like a thousand times more interesting than the current other playable Tyrannid faction. The hardest difficulty has the moderatly retarded decision to double the price of weapon upgrades for your units, making everything that is not a flamethrower not worth the points. While the cleanup phase is less annoying than in Sanctus Reach because the enemies have no morale and will doomrush you even with a single unit alive, there really is no reason for a cleanup phase at all. But still, most of the other 40k games have way more annoying caveats, and the tacticool gameplay isn't half as good to make up for it. Play on max difficulty but disable the option that you have to pay double the point cost for better weapons, you can only do that before you start a campaign.
I feel sufficiently challenged at max difficulty, I lose at least some units every mission, which keeps the snowball effect down enough to make the combat shine.
Also do not get the Necron DLC, unless you want to play them in multiplayer. Horrible value. Spess marine elite DLC is ok, Sanguinary guard is very fun to play. Tyrannid Elite DLC is only good if you want to play nids in multiplayer or procedural campaign.