Child of the Emperor,
Surely, though, you see the disparity between novels where Chaos Space Marines are protagonists and ones where they are not? The Dark Noun series (good one!), for example, features White Consuls non-protagonists that are given some personality and depth. The reverse, unfortunately, is not often the case. Graham McNeill's been the exception, I think, though he accomplished this by sticking to a recurring cast of villains.
To the OP,
Haven't the Horus Heresy novels accomplished that to some degree already, though? At the very least, no one looks at the Alpha Legion, the Thousand Sons, or the Word Bearers the same anymore. Heck, Magnus and the Thousand Sons come off as pretty much sympathetic as a group--even if one doesn't necessarily want to forgive their colossal hubris.