I know people are mixed on the Primarchs coming back.

The foremost Black Legionnaires were mere yards away from the foot of Guilliman’s throne when the rune-panels on Cawl’s auto-reliquary flickered from red to green. A single chime sounded, a clear, pure note that cut through the clangour like a knife. The Archmagos himself, fighting back to back with the Ynnari and Chief Librarian Tigurius, emitted an uncharacteristic blurt of binharic triumph. The next moment, the outstretched armatures of the auto-reliquary folded back with a gaseous hiss to reveal a sight of breathtaking splendour.

Where before Roboute Guilliman had sat, a pale, stasis-locked revenant, now the Primarch stood awake, alert and very much alive. His presence was immense, dominant as a thunderhead suddenly filling the shrine with its crushing pressure. Guilliman was clad in a magnificent new suit of armour, an ornate masterwork that had travelled all the way from the forges of Mars within Cawl’s auto-reliquary. In one hand the Ultramarines Primarch held the blade of the Emperor, lit now from hilt to tip with leaping flames, and in his eyes was a look of such murderous intensity that even the loyalists within the shrine quailed to see it.

It was as though a spell had settled over the shrine. Though outside the din of war thundered on, within that echoing chamber friend and foe alike stared awestruck at the legendary figure reborn in their midst. An incoherent scream of rage shattered the silence, a single Khorne Berzerker charging headlong through the stunned combatants to launch himself in a flying leap at the Primarch. Guilliman moved with such blistering speed that the Ynnari themselves would have struggled to match it. His burning blade drew a pyrotechnic arc through the air as it swung, bisecting the Khorne Berzerker at the waist and hurling his severed halves to the ground.

-Gathering storm Rise of the Primarch.

But as someone who got into the lore when the first Dawn of War came out and having spent so much time in the grim dark of 40k as well as the sadness of reading the Horus Heresy. I genuinely felt complete joy when I first read this. Just like the Ultramarines.