While I don't consider the 40k books on par with the better science fiction out there, I do enjoy that they bring a bit of scale and what it means to space. It's a different take from the rosy, post-scarcity, future of space. Bad things are really bad. Unattended good things turn bad on their own just from drift.

Then there is there is the unashamed embrace of over-the-top in so many different ways.

I've always considered 40k a satire of the entire sci-fi genre (and in many ways a satire on modern politics). In that way, I find it quite refreshing. And your statement of "unashamed embrace of over-the-top" resonates quite well.