Anyway 300 words or less, here we go:
Horus Heresy: Betrayer by Aaron Dembski-Bowden
Betrayer is set around the apotheosis of Angron. Based after the events of Calth Lorgar is allowing Angron to rampage through the Ultramar system unrestrained. Where previously Lorgar was perpetually frustrated with Angron's unpredictable behaviour in this novel he seems to be embracing it.
When I first read the blurb I assumed Lorgar was simply offering Angron up to Khorne as a champion but that's not entirely the case. The reasons behind Lorgar's approach surprised me and I thought it really brought some maturiy to his character that it has long been lacking. I always wondered if Lorgar's fraternal traits would be washed away in one of these novels as he moves deeper into the worship of Chaos but this book took the opposite approach, and I think the overarching Horus Heresy storyline is better for it.
Angron is also portrayed well. There are only so many ways a slavering killer can be framed so any author is working with a limited palette here, but small excerpts within the novel show a character weary of the complexities of politics and trying to escape them by immersing himself in battlefield combat.
My favourite part however would have to be the development of the relationship between Argal Tal and Kharn. Both characters I love because they are honourable at heart but out of loyalty to their Primarch they have ended up on the wrong side of the rebellion. Throughout the book both characters use each other's guidance to maintain sanity and some sense of chivalry as they slip closer to the abyss until a twist at the end turns it all pear shaped.
In conclusion, while the plot may not be all that amazing the character development throughout makes it definitely worth a read.