Signal was a drama that I kept seeing recommended and now that I have finished it, I can see why.
If you're looking for a crime drama that has a great cast and story, then you'll be hooked with this one.

--Spoilers Below--

Park Hae-Yong was such an interesting character. I loved how his story tied in with the overall arc of the story with Lee Jae-Han. I also loved his backstory as to why he became an analyst. He is smart, caring, and good-looking so everything you want rolled into a lead. I'm glad he got his happy ending with both of them and they solved everything together.

Cha Soo-Hyun should've gotten more time with her backstories and story-line in general I feel. It showed glimpses of her and Lee Jae-Han, but that's all it was really. Just glimpses of the two of them and not really any of her own experience. I understand a huge part of her story was missing her partner and the person she loved, but I wish we could've gotten more bad-ass moments of her. You get some of her home life with her sisters and mom... just needed so much more. How happy she looks at the end with the two of them made me so happy.

The glimpses back in time to Lee Jae-Han investigating and his backstory could be quite dry and boring sometimes because you are wanting the mystery solved and for them to figure everything out, but I wish it showed more of him and Cha Soo-Hyun together. I loved the glimpses it did give and loved the way he saw her. It's sad seeing all the people who could've listened to him and even turned on him while he was trying to save lives. I'm glad that he could be happy at the end with the two of them.

Overall, the time loop ending can be a little tricky and took me a while to fully understand what happened and how they all ended up together. It gets mushy with the plot and understanding how that all ties in together with the walkie-talkie, but loved the show and is a great watch.