Unravel Me by Tahereh Mafi- This book was so beautifully written and had some amazing new developments. It's one of my all time favorites.
Everbound by Brodi Ashton- While I enjoyed the first one, Everbound completely blew me away. It surpassed my expectations and I loved how the characters grew.
Of Triton by Anna Banks- This is such a fun series and one that I definitely won't get tired of. The characters, especially Emma, are snarky and especially awesome.
Unbreakable by Elizabeth Norris- This was the sequel that almost didn't happen, lol. Originally, Unraveling was a standalone, but I'm so glad Elizabeth Norris wrote Unbreakable to tie up all the loose ends.
Cross My Heart and Hope To Spy by Ally Carter- The Gallagher Girls series was one of the first YA book series I've ever read and Cross My Heart and Hope to Spy was so much more amazing than the first. My reason why is because a certain character is introduced ;)
Dare You To by Katie McGarry- Pushing The Limits was pretty good, but I liked the characters in Dare You To so much more. The only thing I think might be even better than Dare You To is Isaiah's story ;)
Timepiece by Myra McEntire- I especially like how every book in this series is told in different povs and it's especially cool how it centers around time travel.
The Golden Lily by Richelle Mead-Bloodlines was awesome, but I loved how Adrien and Sydney's friendship grew to be even more in The Golden Lily. The plot definitely picked up speed, too.