Xian Ni is my favorite xianxia series out there so this review would sound biased but believe me this series is really good! Definitely worth a read!
For the first time readers the starting 100-150 chapters might seem bad. I can understand that as those chapters focus on MC's transction from a naive child to a ruthless cultivator. Later on you realize the importance of those chapters when the series take a dark tone. The starting chapters are light hearted and yet tell the dark side of world.
At start MC is hesitant to kill even after learning that the world follows the law of jungle.  Er Gen smartly wrote the transction between a naive child to a ruthless cultivator.  You could actually feel the hesitancy MC shows as he steps on the dark side. Later on he becomes totally ruthless but the starting of series provide the reasons.
The cultivation levels are impressive as well. Unlike other novels cultivation levels in Xian Ni are unique.  Each cultivation level give different powers. Cultivation isn't as easy as storing massive amount of energy/qi to power-up. You have to sever your spirit, transform soul, seek Dao, etc...
The best part is that author doesn’t waste many chapters on training after the first 200 chapters! Other xianxia are of 60% training but Xian Ni is full of adventures! Those adventures are unique and author gives strong foreshadowing of future troubles.
Some would say that it's a revenge story. Believe me this is not the usual stupid revenge tale. Xian Ni is 2K+ chapters but the revenge part hardly last for 100 chapters and even im those chapters more than 50% of them are focused on adventures.  In other tales you always root for MC but in Xian Ni you would actually feel sad for the bad guys. The revenge arc was full of bittersweet moments.  Really impressive.
Er Gen is a genius when it comes to creating unique abilities.  Wang Lin's fights never bore you. The best part is that author doesn’t waste chapters for character shilling unlike other popular novels.
World building is impressive as well. There are different types of cultivators and there are many planets. Even the current planet in which Wang Lin is residing in is full of mystery. There are star systems which would be explored in future chapters.
The most unique part of the series is that Wang Lin's life is full of tragedy unlike other xianxia.  Sure MC is lucky in cultivation but he's hardly happy.  The storyline is grim and even the death of minor characters would make you sad.
You should definitely give this series its well deserved chance. Believe me this is the most unique xianxia out there.