I'll be honest - I picked up this drama because I'm an OCN fangirl, and I'll do the same for the one after it. I was unfamiliar with the leading actors, and was unsure after the first episode. Alas, I stuck through and I'm glad I did.
If you've watched "Signal" (if you haven't - what are you doing?!), you might think that the premise sounds a bit familiar, though the dramas don't have that much in common. In my opinion, "Signal" was a better crafted drama with less plot-holes/the-police-is-too-dumb moments, however "Tunnel" is still a drama that deserves a chance.
One of the things that stood out to me in this one was the main female lead, something that I've disliked with OCN's dramas are their stupid and useless female characters (though, to be honest the rest of kdramaland is no better), however, Shin Jae Yi has been the exception for me. Sharp, smart, and unrelenting, she was a great female character that held my attention alongside the male duo.
This drama's weakness comes towards the end, just like "Voice", it began to fizzle out, with too many police stupidities and too many instances of Park Kwang Ho, the main character, just yelling "bastard" over and over. It was hard for me to get through episode fourteen but I'm glad I did. The ending wasn't as sharp as it could've been, and it wasn't unique like how I would've wanted it (but I do like sad and torturous endings), but it was a heart-warming one.
"Tunnel" is not a perfect drama but it's a good addition to the ever-growing crime genre in Korean dramas. I recommend giving it a try, but be ready to be at the edge of your seat each episode, and be warned that you'll probably spend sixteen hours in front of your screen because it's hard to stop watching one you start.