OCN is well-known for its dark/mysterious/psychological/detective/thriller dramas. Indeed the dramas telecast in this particular channel are always more or less enthralling. Once seated with an episode, a viewer (mainly who love this sort of genre) would finish all the episodes in rapid succession leaving himself/herself unkempt at the end. Yes, it happened to me after I finished Tunnel in one sitting for two days. After the last and final episode I just couldn't see myself in the mirror. Well that doesn't necessarily mean this drama is a perfection or a masterpiece. Despite having number of flaws and loopholes, it could live up to my expectations. Although practically the concept of time traveling is superfluous and unrealistic but the integration of both past and present to solve the crime is riveting yet not extraordinary. As a viewer I appreciate the way the writers managed to maintain a cliff-hanger per episode and how one by one a particular mystery unraveled. Any sort of art/literature/entertainment can be preposterous but to make it credulous to the viewers is where the makers can show their creativity. All the credit goes to the scriptwriters who managed it pretty nicely. In the beginning, few episodes have individual crime story which were solved meticulously by the detective team, however, the main story was there and gradually each puzzle pieces were weaved in a single thread. Though all the bits and pieces were scattered initially but the story maintained coherence till the end. Much confusion was not created with the time traveling factor. The whole drama is like a web of riddle solved rigorously. Overall the story writing was commendable but during episodes 12-16 it became excessive. For instance, if we squeeze too much lemon juice in our rice rather than giving a slight sour flavor, the whole rice would turn bitter in taste. This is what happened with Tunnel during these episodes. The flow was fascinating but due to excessive twists and turns for finding the main culprit, it kind of lost the ultimate thrilling essence in the middle part in my opinion. One interesting thing is, they tried to depict prisoner's dilemma (a concept of game theory in economics) in a theft case but did not show it vividly. I can remember clearly this whole concept was portrayed exquisitely in the drama named "I Hear Your Voice". On another note, indignation is inevitable upon any murderers or in general any wrong doers, nonetheless it made me ponder upon a particular thing. That is, giving a child a healthy and fine environment to grow up is extremely crucial. It is true that all the heinous murders took over negligible issues but when the culprit was a little boy from then on he had nurtured grave darkness inside him. From his early childhood the unsound experiences he gathered, later triggered him to exploit himself in a psychotic manner towards gaining aberrant pleasure. It all comes down to the upbringing, nurturing and giving a child a loving environment. Compassion can change a person at a tender age. Moreover, I appreciate the depiction of the female character, Professor Shin Jae Yi. For goodness sake, they refrained for at least once by not showing a sassy, unintelligent and screaming woman. Shin Jae Yi is stoic but a smart, competent and educated woman who came up with brilliant clues regarding solving the cases. Loved the tough at the same time sweet bromance of Gwang Ho and Sun Jae. Love the comradeship among the fellow colleagues. As I always say Korean writers are best at portraying human relationship and emotion among each other. Hats off to the writers for that. All the casts more or less shown good acting skill though not phenomenal. Necessary to mention that the last episode is utterly heart wrenching and is beautifully wrapped up. Especially visiting every victim's home and paying respect to each of their family was wonderfully done. This little message "Saving Life is important" is laudable. On the other hand, background score is reasonable with the situation and I could find only one OST named Circle of Life by Kim Dong Uk. It's soft rock which gets slightly heavy at the end sounds superb. In conclusion, this drama has the characteristics to put a viewer at the edge of their sit but comes with few flaws. If the errors and flaws can be overlooked, it's pretty interesting. I felt like I have completed reading a thriller novel. For a crime drama genre lover, I don't think it would be a bad choice for giving it a shot.