Gigachad Well, they're all reasonably well-written and none of them ever felt like a slog to read. I'm definitely going to get to the rest of Abnett's Sabbat Worlds books eventually, Double Eagle really got me into the whole scenario. but I like to try not to read books focused on the same faction in a row. Right now I'm moving between continuing the Horus Heresy series (last I read was Prospero Burns), the Path of the Eldar series (finished reading Path of The Warrior earlier this year) and the Shira Calpurnia series. I've already decided my next 40K novel is gone be Blind, which is the last Shira novel. I probably should have mentioned Shira's trilogy in the last post, come to think of it. Having a police action movie plot set in the WH40K universe is a pretty neat idea and the stories of the first two books were pretty fun too. They're full of cool little subplots like one where the daughter of a local big time rogue trader that was promised to marry into another house decides to join the Sisters of Battle and take a vow of chastity, and then said rogue trader flips his lid and threatens to bombard the SoB convent if they don't hand over his daughter back.
Also, I don't think you should let not knowing about a faction keep you from reading their novels, they're never written in a way that you absolutely need tons of background knowledge to understand/enjoy the stories. If anything they're a pretty good way to get to know the factions.