PhillyT - It depends on the Author...
Dan Abnett has done a nice job of a 40k lite world, where it isnt quite so horrid, plus he is an ok writer, but it is far from the fluff written in the army books and such like.
The other authors are more like the army books, being a full on case of the "mary sue" in many cases.
Much of the best stuff is actually from a much earlier period, when it had a dark, baroque feeling (Ian Watson's early stuff, fluff from the two "Realms of Chaos" books) and it only tends to be in the later period that fluff has utterly contradicted each other
The recent Horus Heresy novels have been hit and miss, when I get chance I will look at who has written the good ones and the bad ones...