Fair enough, they do take a different tact than most Space Marines. As a Blood Angels fan though, I may have a slighty biased opinion. I've seen them written decently (although maybe not as interesting.) James Swallow is the worst sometimes and I regret the Blood Angels are "his" to write for. What sometimes get me about the Flesh Tearers is being contrarian is their keynote feature. The HH set up that since Amit was just a disagreeable bastard, that being Negative Nancies is now part of their culture, the whole "loyal opposition" thing. It stands out but it doesn't necessarily make them interesting to me. Like, because writers dig the Space Viking theme so much they've generated a lot of material for Space Wolves that they can draw on for inspiration to inform both individual traits of Space Wolves and attitudes the Chapter as a whole has as well. There's a richness there that is totally absent from a lot of other chapters.
For example, Blood Angels hail from Baal Secundus and it's a rad-wasted desert world and giant radioactive scorpions and shit. It informs the Blood Angels to the degree that they started humble and then became elevated to god-like statuesqe beauty and grace. And so they have a more grounded perspective on the posthuman condition because they empathize with humanity more than a lot of chapters, and so they take a more noble stance.
Now staple a "dark, bestial secret" to that and the general characteristic of the Blood Angels is noble, angelic, tragic figures. But that's pretty much the end of it. So within that total sphere of ideas and inspirations, you end up with a handful of archetypes.
See, when you get a Space Wolf character who actually cares sincerely about human life and is thoughtful and observational things, maybe is a little soft, that's unique given what Space Wolf culture is usually like. It's a character you can remember for their habits and beliefs. Compare that to Ultramarine #996 who, like the rest, is duty bound, intelligent, articulate, progressive, honorable, a master tactician, who tend to get real mad when things don't go their way.
The most common way I've seen authors try and inject some personality into Space Marines is to always set up one guy as the "bad guy" within a chapter. One guy who is just kind of an asshole or arrogant. If you're lucky they've got at least a believable motivation for being so, but often they're just written to be as unlikable as possible (within the context of a Space Marine chapter) so the main character/hero Marine stands out and looks better by comparison.
I guess for an IP that pumps out this much fiction, it's inevitable that a lot of it is just going to hammer on the same tropes for the most part, since they're so well established. It's just a disappointment sometimes, and why I think Space Marines bore the shit out of people, because writers do so little with the ideas sometimes, and fail to really put themselves in the shoes of a posthuman and then work that idea from different angles within each chapter's history/context.