It's fascinating to me that you find Huxley a slog. Is it the language? I don't consider it a great book but I've probably coverIIcover'd that thing three or four times just because teachers have a hard time arguing with anyone's interpretations, so it's a perfect lazy student's fallback. I once re-read it and vomited out a 500 word essay (longhand, in pen) in the six hours it took to make it home from Colorado in the back of a van. I've never played Warhammer. I played Battletech and my cursory spot-check found their novels to be largely ghastly. That said, what ones I tried clearly owed the whole of their existence to The Forever War, which is worth being familiar with.
Huxley is interesting, with a lot of ideas thrown from the get go, and it's more likely my current workload and family bullshit at the distance preventing me from enjoying the story. I rarely don't give a book multiple chances, so we'll see. Right now, it's flatter than my color perception, but the language isn't a problem. re 40k: I usually recommend people start with Sandy MItchell's Ciaphas Cain books, who's pretty much Blackadder given a role of a commissar (political/morale officer) and a gun to execute morale problems. Comedy of errors/accidental hero is a good framing for grimdark.