Semi-rant: I like the direction 40k is taking
So perhaps its because I have only recently gotten into this fandom (about a year ago) but I actually like the fact that Guilliman and Cawl are making reasonable/progressive changes to the Imperium. These changes include:
-Better technology (grav tanks, new power armor, new space ship upgrades, plasma guns that are 100% reliable, better dreadnought armor, better boltguns etc.)
-Better governance (re-formation of Ultramar into the 500 worlds, recreation of the tetrarchy, Guilliman’s efforts to write a treatise on good governorship etc.)
-Alliances/Dialogue with Xenos (Guilliman’s working relationship with the Ynnari, possible non-agression treaty with the Tau)
While a lot of people say that the setting is ruined because of these things, I would say that its actually improved because it adds diversity of thought to the Imperium.
If you want a completely grimdark Imperium that wants nothing more than to kill the xeno, traitor and heretic, who mainly uses older types of weapons and fanatically worships the Emperor as a God; then there’s a large portion of the Imperium holds these beliefs already (probably on the Imperium Nihilus side of the rift).
However, if you want a more reasonable and forward-thinking Imperium where there is an effort made toward techological progress etc. you could look at Ultramar or other places where Guilliman and Cawl have strong influence/rule over.
I don’t really want to sound entitled here but to be honest, I’ve been looking for a faction in the Imperium that thought the way the latter did ever since I got into the setting. Its part of why I became heavily invested in the Ultramarines and their efficiently run star empire of Ultramar. Now I’m finally starting to get something like that and I’m happy with it.