Do not expect that you will be given an ending that is different. Most comment about how predictable the story was. Of course it was predictable, the plot has been so open and clear about the relationship of Choi Mujin and Yoon Ji Woo. What this drama aims is to show how Ji Woo endured everything and why she chose to do what she did in the ending.
Everything is about trust. The Organization was established and lasted for years because of the loyalty of the members, bringing in the picture of Yoon Donghoon. Donghoon stayed with the police even though Mujin showed unwavering loyalty. That was the moment the trust was shattered between Mujin and Donghoon, someone died.
Then enter Yoon Ji Woo. Ji Woo trusted Mujin, but this time, it was Mujin who used and confused Ji Woo. Another trust was shattered, leading to the ultimate death.
In the last episode, Mujin mentioned that Donghoon was meant to be a prey. He hesistated to kill Mujin even though he has a lot of chances to do so. But if we look at it overall, Mujin, who was once a predator, became a prey in the presence of Ji Woo. It was also his hesitation to dispose and kill Ji Woo that led him to his death in the hands of Ji Woo. Both cases have similarities. Donghoon hoped to reform Mujin by eventually bringing him in the hands of the law, which can be mirrored to Mujin wishing for Ji Woo to turn her back from the police and execute her revenge in the way the organization does things.

I still kept on coming back to My Name. It's rare for me to rewatch a drama, but you would appreciate My Name the most after rewatch. There are things that you might have missed the first time probably because you are not yet familiar with all the characters. Another beauty of rewatching would be noticing the hints and clues dropped in every episode about their fate, which didn't mean anything at first watch.
Lastly, this is probably the best performance of So Hee, she is just so tailored for action.