Seems like this trilogy got better with each book - pacing in this book felt just right. The twist(s) aren't predictable - they make sense given original information, but aren't coming out of the blue either / match previous hints. 
 An interesting love quadrangle (for once) 
 It's not all about the feels - the future of a nation is at stake. All three potential love interests had a different, compelling appeal: 
 - Mal, her lifelong friend and loyal confidant; 
 - The Darkling, the only other Grisha who understands the unique pressures of great power; 
 - Nikolai Lantsov, the silver-tongued and impeccably confident prince with a helpful army and funding. 
 (I'm fascinated by political marriages in history, so this was the choice I was rooting for. Not that Nikolai would have been the most romantic option, but certainly an interesting one! I would have read a whole book about Alina & Nikolai's friendly political marriage coexisting tenuously with Alina & Mal's actual-life-partner relationship.) 
 Stunningly beautiful settings 
 Leigh Bardugo's world-building is top-notch. I'm glad that DreamWorks has picked up the rights to make this trilogy into a film, because some of the scenery in Ruin and Rising sounded pretty awe-inspiring. 
 As a few examples: 
 - The network of caverns and passages curling away from the White Cathedral, each of which bears a distinctive name like the Jewelbox, the Orchard, and the Angelgate. 
 - The haunting beauty of the Firefalls at sunset. 
 - The glass-domed Spinning Wheel, built atop an ancient pilgrimage site and decorated with bronze columns representing the constellations 
 Decently complex characters 
 - The Darkling commits unspeakable acts yet remains deeply human, craves company with his "peers" 
 - Good development of personalities of side characters. friendships that feel like they were built over time, hits all the right emotional notes without becoming maudlin