I have seen the books you mentioned and though about those a great deal, however, I wasn't sure if I really cared for imperial guard stuff, but the story line is more important to me.
Gaunts Ghosts is the only one of those that is Imperial Guard based. But it's imo a truly fantastic series. The beauty of it being that it is quite big, so you do end up knowing and loving the characters quite a lot as you go, which makes their triumphs and casualties that much more meaningful, or so I found anyway.
Eisenhorn, Ravenor, Bequin, are so good because they show you the side you never see of the Imperium. The actual worlds, cities, politics and behind the scenes machinations. These novels aren't set on battlefronts or in the middle of giant wars and campaigns. They're on the ground, investigating leads, getting amongst Imperial society and politics, but with good solid action mixed in.
The Night Lords trilogy is so good I suppose, because it really get's you attached to these traitors, and some of the most brutal ones at that, yet still makes them protagonists in there own way.
On that same note, I knew I was missing one book out, and it's a truly unforgivable miss. I would put it up there in the top spot with others as one of the best books BL have produced and overall one of the best books I have read myself. Like the Night Lords, it focuses on traitors, but makes them into very sympathetic characters somehow in some cases and just downright likeable. It is a must read in every way, and the series will no doubt only get better. That book?
The Talon of Horus.