I've never seen Jing Bo Ran in anything before, but as ML Lu Chen he was excellent. He wasn't cold, he was stoic. But his heart was on his sleeve for Gui Xiao from day one! Okay, you can never go wrong with a man in uniform, so that was bonus. His stature and demeanor were such that you totally bought him as soldier/police. But being the romantic I am, I loved all of his scenes with the FL. The small gestures were a testament to his love for her. Closing his eyes when hugging her, burrowing his head into her neck like he just loved the essence of her, the kiss in her hair when they hug. Every action was butterfly-inducing.
I love Tan Song Yun and she was lovely as Gui Xiao. She is a good actress, she's so beautiful, she is a beautiful crier.
Their chemistry was amazing! Bo Ran has very expressive eyes and manages to convey so much love using just his eyes. And when he smiles, my oh my! Lots of wonderful kisses and hugs. The scene where his back is to her and asks her to take his hand - beautifully filmed and so tender. They were yin and yang. She was so bubbly and effervescent, and he was serious. I can't stress enough how much I loved this couple together.

Big bonus - thank you SO MUCH for not adding the conniving female trying to break them up, or the sad/morose male that loves her from afar. This truly was a drama about them and the strength of their love.

The second couple was cute to watch.

So why is my score so low, after waxing poetic about the strength of the leads?
1) There is SO MUCH filler in this drama!! They spent an inordinate amount of time showing the training and the missions of the SWAT team. I couldn't quite figure out if it was patriotism or propaganda. All that extra stuff took up at least half of the drama.
2) The flashbacks. There were, I think, three different years that they kept flashing back to. I didn't think that the flashbacks were used effectively, especially since the actors pretty much looked the same once they got out of school. The last episode's flashbacks finally gave us the whole history of their relationship, which was nice to see, but then the drama just ended!
3) This might be just a translation issue, but she asks if he still remembers her and he says, "I'd still remember you if you turned to ashes." They showed this a couple of times, and the wording is just a little creepy to me.

I can highly recommend this drama for the main couple. Plus, you might not be bothered by all the time spent on work stuff, but I didn't find it interesting.