New fluff is stupid. It's all one huge asspull that doesn't seem to tie well with previous fluff. First they introduce a way to stop Chaos, then they break that way and send Imperium into giant-ass state of "it's over son" only to asspull Primaris that save the day. Not to mention the entire feel of WH40k goes away from "lmao scraping the barrel but there's still hope" to "HIGH TECH TAU GET REKT". Not to mention Primaris design is eh. Have you looked at Reivers? Sure, skull helmets were a thing before but it had a reason apart from "i'm edgy totally not-night lord". I don't really even know. Wh40k was never specifically known for subtle design, and the same could be said for a lot of things before, but right now looking at half the stuff that's new it just screams "G.I Joe" or other action figurines. I mean, the baseline Primaris is okay, I guess (even if I'm sad Errant pattern, the previous evolution of Space Marine armour is now absolutely forgotten because before it even had time to be issued it's replaced by Primaris), but Reivers and Primaris Chaplains strike me as... going over the line. Sure, as I said, skulls, edgy imagery, but I felt there was a bit of difference between previous style which was more golden, decorative, invoking the gothic style and some of weirder historical stuff like various catacombs (or various chapels of skulls like Sedlec Ossuary, but I've been to two less known ones in Poland), the medieval cult of death, and so on, and current style which seems to invoke more high-tech but edgy stuff. Chaplains now look like fucking Reaper from Overwatch, for all it's worth.
I may be just rambling and dislike the new stuff because it's, well, new, but the feeling from I got from Warhammer before was taking the stereotypical view of "Dark Ages", kicking it to extreme and putting it into space, and then just adding everything else to the mix so there was a bit of everything, but over-all style was gritty, dark and toned down, with periodical sparks of greatness and of course remembrance of amazing Golden (quite literally) Age of yore. Right now it's a wild train of fuck knows what that I'd think is more compliant with fucking Star Craft or other absolutely generic Science-Fiction, except with throwing in some edge as an afterthought because "oh right it's still Grim Darkness of Far Future".