Thunder and Steel is a collection of different Dan Abnett Warhammer material; mostly novels and short stories, but with a few graphic novels thrown in as well. Not all of it is all that great, but some of the stories are well worth the purchase. The omnibus contains a bit of a rant from the Dan, mainly about when, why and how he wrote the stories, a feature which I personally find very enjoyable.
The two first novels in Thunder and Steel are Gilead's Blood and Hammers of Ulrich. Both of them started out as a collection of short stories, which have later been worked into novels. Unfortunately, it shows. Especially Gilead's Blood is rather disjointed. It is also, very clearly, from the earlier days of the Warhammer universe. The style of the stories has changed since then and to my mind, Gilead's Blood is the weakest of the novels in the omnibus. It took me quite a while to chew my way through it, I'm afraid. Hammers of Ulrich works somewhat better, even though it is a joint venture between several authors. At times it is pretty great, but overall it doesn't quite reach the mark. The third, and last, novel in the omnibus is Riders of the Dead, which in my opinion is the best part of Thunder and Steel. This is the novel that makes the omnibus worth buying. The final two shorts stories (Swords of the Empire and Shyi-zar) work. They aren't great, but they are well worth a read as well.
The last 30 or so pages are given over to graphic novels and, frankly, they shouldn't have bothered. Now, I'm not a big fan of Black Library's graphic novels, so I don't really know how well the graphic novels worked originally, but in grainy black-and-white and printed on small pages in a paperback; they simply don't work on any level.
All in all, I sort of liked Thunder and Steel, but it does have a few problems, which makes me feel it only deserves three stars.