Farseer

Rogue Trader Janus Darke is a desperate man. Once rich and famous, a string of bad luck has brought him to the brink of ruin. Dreaming of past glories, lost in despair, the last thing he wants is to accept a commission from two mysterious strangers – a voyage to the Eye of Terror, the dark heart of the galaxy. But Janus finds himself in more danger than he could have ever imagined, as he is pulled into the middle of a deadly power struggle between the elder and their ancient enemy, a daemon prince of Slaanesh.

Read it because
It's the original eldar novels, from one of the minds behind the early development of Warhammer 40,000. It's a wild and sometimes wacky adventure, and it's packed with moments both chilling and revelatory.