Storm of Iron

Storm of Iron - Graham McNeill Standalone Warhammer 40K novel, I think it was one of the first to tell the story from the Chaos Space Marines point of view.

A barren planet, defended by local Imperial Guard forces finds itself under attack by the Iron Warriors.
Below the Warsmith, there are three main characters all vying for his attention, and that of the Chaos gods.

There's a lot going on all through the book. The Imperial Guard are outgunned and unprepared for what they have to face. Even with help from some Imperial Fist marines, things are stacked against them.

This was a good story, lots of action and interesting characters on both sides.