This drama was unnecessarily long. It could have ended after a maximum of 25 episodes. The premise was great but unlike other second chance shows where the protagonist has a second chance in life and goes back in time to change life and make it better for himself or his loved ones, this one didn't really achieve that. Halfway through, it suddenly introduced new characters as if just to prolong the drama. The overarching mystery was interesting but too drawn out. The high school friends had a good thing going and their chemistry was great, but they were very single dimensional. Far more could have been achieved with them given that it was a 40 episode drama. In short, watch it only if you are out of dramas to watch, otherwise other second chance dramas such as Still 17, Go Back Couple, and 18 Again, are far better.