Xenos by Dan Abnett was a cheeky comfort reread over Christmas. I first read it in the first year of university and it was already old then and now it’s 25 years old. Old enough to have opinions on amasec vintages.
Do I recommend it? Hell yes. It’s the way to get into 40K fiction, you could probably just read the Eisenhorn series and leave the rest of the 40K extended universe. I’ve got a couple of other books on the go at the moment to might hold off on starting the sequel for a bit.